Tropical Cyclone Donna

[Manukau heads obs]

not what New Caledonia wants to hear

[Nev]

TC Donna was upgraded to Cat 4 by RSMC Nadi around 1pm today, with a central pressure of 963 hPa and mean-winds of around 170 km/h. In contrast, JTWC has actually reduced its estimated winds a little, due to a significant weakening of convection earlier, although that has returned in recent hours and JTWC expect her to continue to reintensify over the next couple of days.

TROPICAL DISTURBANCE ADVISORY NUMBER A13 ISSUED FROM RSMC NADI
May 060212 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 963HPA WAS LOCATED NEAR 13.3S
163.7E AT 060000 UTC. POSITION POOR BASED ON HR HIMAWARI-8 EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE WEST SOUTHWEST AT
ABOUT 07 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE
ESTIMATED AT ABOUT 90 KNOTS.

DEEP CONVECTION REDUCED IN RADIAL EXTENT DUE TO DRY AIR ENTRAINMENT
FROM EAST. ORGANIZATION REMAINS GOOD. SYSTEM LIES JUST NORTH OF AN
UPPER RIDGE IN MODERATE SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 29 DEGREES CELCIUS. SYSTEM STEERED WEST SOUTHWEST
ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH. DVORAK ANALYSIS
BASED ON EMBEDDED CENTER WITH LG SURROUND, YIELDS DT=4.5, MET AND PT
5.0. FT BASED ON MET. THUS YIELDING, T5.0/5.5/D0.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 061200 UTC 13.6S 163.5E MOV SSW AT 02 KT WITH 85
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 070000 UTC 14.2S 163.5E MOV W AT 02 KT WITH 80 KT
CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 071200 UTC 15.3S 163.6E MOV S AT 03 KT WITH 80 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 080000 UTC 16.4S 163.8E MOV S AT 04 KT WITH 75 KT
CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 060800 UTC.

WTPS31 PGTW 060300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 010//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 010
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
060000Z --- NEAR 13.1S 163.9E
MOVEMENT PAST SIX HOURS - 315 DEGREES AT 06 KTS
POSITION ACCURATE TO WITHIN 060 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 085 KT, GUSTS 105 KT
…
REMARKS:
060300Z POSITION NEAR 13.1S 163.8E. TROPICAL CYCLONE 18P (DONNA),
LOCATED APPROXIMATELY 375 NM NORTHWEST OF PORT VILA, VANUATU, HAS
TRACKED NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) REVEALS A SIGNIFICANTLY
WEAKENED CONVECTIVE SIGNATURE, WITH THE PREVIOUSLY ESTABLISHED
CENTRAL COLD COVER (CCC) HAVING COMPLETELY DISSIPATED, WITH ONLY
PATCHY MODERATE CONVECTION. AS OF THE LATE 0000Z HOUR, SIGNS OF
REDEVELOPMENT OF DEEP CONVECTION HAVE APPEARED, BUT IT IS TOO EARLY
TO DETERMINE IF THIS WILL STICK. THE INITIAL POSITION IS PLACED WITH
MODERATE CONFIDENCE BASED ON ANALYSIS OF THE AVAILABLE HIGH
RESOLUTION VISIBLE IMAGERY AND A 2156Z AMSU 89 GHZ MICROWAVE IMAGE
AND COINCIDENT ASCAT-B PASS, WITH A WELL DEFINED LOW LEVEL
CIRCULATION CENTER (LLCC), STILL SHIELDED FROM VIEW BY UPPER-LEVEL
CLOUD COVER. THE INITIAL INTENSITY OF 85 KNOTS IS BASED ON
ASSESSMENT OF REPORTING AGENCY AND AUTOMATED DVORAK CURRENT
INTENSITY ESTIMATES BETWEEN 4.5 AND 5.0 AND SUPPORTED BY THE OVERALL
WEAKENED APPEARANCE OF THE SYSTEM. BASED ON ANALYSIS OF THE UPPER-
LEVEL DATA, THE RECENT WEAKENING PHASE WILL BE SHORT LIVED, AND WAS
DRIVEN BY AN INCREASED NORTHEASTERLY UPPER-LEVEL FLOW OVER TOP OF
THE SYSTEM. RECENT ANALYSIS INDICATES A SHIFT FROM THIS
NORTHEASTERLY FLOW PATTERN TO DEVELOPMENT OF AN UPPER-LEVEL POINT
SOURCE IN THE NEAR TERM. THE OVERALL ENVIRONMENT REMAINS SUPPORTIVE
OF INTENSIFICATION WITH WARM SSTS NEAR 29 CELSIUS, A STRONG POLEWARD
OUTFLOW CHANNEL AND LOW TO MODERATE VERTICAL WIND SHEAR (VWS) VALUES
BETWEEN 15-20 KNOTS. OVER THE PAST SIX HOURS, TC DONNA HAS CONTINUED
TO TRACK WEST-NORTHWESTWARD UNDER THE INFLUENCE OF AN ELONGATED
SUBTROPICAL RIDGE (STR) AXIS ALONG TONGA TO NEW CALEDONIA TO
NORTHEAST AUSTRALIA AXIS, WHICH CONTINUES TO INHIBIT SOUTHWARD
MOVEMENT AT THIS TIME. THIS RIDGE IS EXPECTED TO BREAK DOWN AND
REORIENT TO A MORE NORTH-SOUTH AXIS BY TAU 24, ALLOWING TC DONNA TO
TURN POLEWARD AND ACCELERATE THROUGH THE REMAINDER OF THE FORECAST.
AS THE AFOREMENTIONED POINT SOURCE DEVELOPS OVER TOP OF THE SYSTEM,
ENVIRONMENTAL CONDITIONS WILL BE RIPE FOR FURTHER INTENSIFICATION
THROUGH TAU 48, PEAKING AT 110 KNOTS BEFORE BEGINNING A WEAKENING
TREND AFTER TAU 72 AS VWS INCREASES AND SSTS DECREASE. TC DONNA WILL
BEGIN TO UNDERGO EXTRATROPICAL TRANSITION BY TAU 96 THROUGH THE
REMAINDER OF THE FORECAST. NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT WITH EGRR REMAINING AS THE SOLE EASTWARD OUTLIER, LEADING
TO HIGH CONFIDENCE IN THE JTWC TRACK FORECAST. MAXIMUM SIGNIFICANT
WAVE HEIGHT AT 050600Z IS 30 FEET. MAXIMUM SIGNIFICANT WAVE HEIGHT
AT 060000Z IS 30 FEET. NEXT WARNINGS AT 060900Z, 061500Z, 062100Z
AND 070300Z.//

[Nev]

I think Donna sets a record as the only May TC to reach Cat 4 since satellite records began in 1970.

There's also only been 2 other Cat 3 TC's in May, Ida in May/Jun 1972 and Namu in mid-May 1986, both around the Solomons - TC Namu was one of most devastating and deadly to have ever hit the region.
(there were also 2 Cat 3 TC's in June)

[Thunder081]

I think Donna sets a record as the only May TC to reach Cat 4 since satellite records began in 1970.

There's also only been 2 other Cat 3 TC's in May, Ida in May/Jun 1972 and Namu in mid-May 1986, both around the Solomons - TC Namu was one of most devastating and deadly to have ever hit the region.
(there were also 2 Cat 3 TC's in June)

Interesting

[Manukau heads obs]

an eye showed up overnight, has gone again...and the eye is cartwheeling around (looping)
which the cyclone has been doing for a while now, hence the zig zag movement

[Nev]

Nadi now have Donna back down Cat 3. Earlier this morning they had extended Donna's expected Cat 4 reign until tomorrow, which is more inline with JTWC's forecasts.

Yes, Donna revealed a 22 km wide ragged eye to infrared imagery earlier last night before becoming cloud covered again. I think the zig-zag effect on Nadi's track maps might be a little exaggerated, due to not being able to get an exact fix at the time on Donna's mostly hidden eye, as JTWC's maps don't show quite the same effect?

TROPICAL DISTURBANCE ADVISORY NUMBER A16 ISSUED FROM RSMC NADI
May 062007 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 960HPA WAS LOCATED NEAR 13.6S
163.9E AT 061800 UTC. POSITION POOR BASED ON HR HIMAWARI-8 EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE SOUTHWEST AT ABOUT 1
KTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT
ABOUT 85 KNOTS.

EYE CLOUD FILLED WITH DEEP CONVECTION OVER LLCC. ORGANIZATION REMAINS
GOOD. SYSTEM LIES JUST NORTH OF AN UPPER RIDGE IN MODERATE SHEARED
ENVIRONMENT WITH GOOD POLEWARD OUTFLOW. SST AROUND 29 DEGREES
CELCIUS. SYSTEM STEERED WEST SOUTHWEST ALONG THE PERIPHERY OF A MID
LEVEL SUBTROPICAL HIGH. DVORAK ANALYSIS BASED ON EMBEDDED CENTRE WITH
BLACK SURROUND YIELDS DT=5.0, MET AND PT AGREE. FT BASED ON MET. THUS
YIELDING, T5.0/5.5/S0.0/24HRS.

FORECASTS :
AT 12 HRS VALID AT 061200 UTC 13.6S 163.5E MOV S AT 04 KT WITH 85 KT
CLOSE TO CENTRE
AT 24 HRS VALID AT 070000 UTC 14.2S 163.5E MOV S AT 05 KT WITH 80 KT
CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 071200 UTC 15.3S 163.6E MOV S AT 06 KT WITH 80 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 080000 UTC 16.4S 163.8E MOV S AT 06 KT WITH 75 KT
CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 070200 UTC.

WTPS31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 012
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
061200Z --- NEAR 13.5S 164.1E
MOVEMENT PAST SIX HOURS - 205 DEGREES AT 02 KTS
POSITION ACCURATE TO WITHIN 025 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 090 KT, GUSTS 110 KT
…
REMARKS:
061500Z POSITION NEAR 13.7S 164.0E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 350 NM
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTH-SOUTHWESTWARD
AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS A RAGGED 12-NM EYE WITH IMPROVED
CONVECTIVE STRUCTURE. HOWEVER, THE MOST RECENT EIR IMAGERY INDICATES
THAT THE EYE HAS FILLED. A 061113Z METOP-A 89 GHZ IMAGE SHOWS THE
BULK OF DEEP CONVECTION IS CONFINED TO THE NORTHERN SEMI-CIRCLE WITH
AN ASYMMETRIC MICROWAVE EYE FEATURE POSITIONED ALONG THE SOUTHERN
EDGE OF THIS DEEP CONVECTION. BASED ON THE EYE AND RECENT MICROWAVE
IMAGERY, THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION. TRACK
MOTION REMAINS SLOW WITH A SLIGHT SOUTHWARD DRIFT. THE CURRENT
INTENSITY IS ASSESSED AT 90 KNOTS BASED ON DVORAK ESTIMATES OF T5.0
FROM PGTW, PHFO AND KNES. TC 18P IS CURRENTLY LOCATED WITHIN A
COMPETING STEERING ENVIRONMENT BETWEEN A WEAK SUBTROPICAL RIDGE
(STR) OVER NORTHEAST AUSTRALIA AND A STRONG STR TO THE EAST. THE
WESTERN STR IS FORECAST TO WEAKEN SIGNIFICANTLY AS A DEEP
MIDLATITUDE TROUGH DEEPENS ACROSS THE CORAL SEA, WHICH WILL ALLOW
THE EASTERN STR TO BECOME THE DOMINANT STEERING INFLUENCE WITHIN THE
NEXT 24 TO 36 HOURS. TC DONNA IS FORECAST TO INTENSIFY TO A PEAK OF
110 KNOTS UNDER FAVORABLE CONDITIONS TO INCLUDE WARM SST, LOW
VERTICAL WIND SHEAR (VWS) AND ROBUST POLEWARD OUTFLOW. AFTER TAU
36, TC 18P SHOULD BEGIN TO ACCELERATE SOUTHWARD AS IT TRACKS ALONG
THE WESTERN PERIPHERY OF THE STR. GRADUAL WEAKENING SHOULD OCCUR AS
THE SYSTEM TRACKS OVER COOLER SST. NEAR TAU 72, TC 18P WILL BEGIN
EXTRA-TROPICAL TRANSITION AS IT INTERACTS WITH THE MIDLATITUDE
WESTERLIES AND A WEAK BAROCLINIC ZONE. THE SYSTEM WILL ACCELERATE
SOUTHEASTWARD AFTER TAU 72 AS IT COMPLETES EXTRA-TROPICAL TRANSITION
AND BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES. DYNAMIC
MODEL GUIDANCE IS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH
CONFIDENCE IN THE JTWC TRACK FORECAST. DURING THE EXTENDED PERIOD,
TC 18P WILL WEAKEN RAPIDLY DUE TO INCREASING VWS AND COOL SST LESS
THAN 25C. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 061200Z IS 30 FEET. NEXT
WARNINGS AT 062100Z, 070300Z, 070900Z AND 071500Z.//

[Nev]

JTWC still has Donna intensifying and peaking tomorrow, but not by quite as much as earlier forecasts…

WTPS31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 013//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 013
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
061800Z --- NEAR 13.4S 164.1E
MOVEMENT PAST SIX HOURS - 180 DEGREES AT 02 KTS
POSITION ACCURATE TO WITHIN 060 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 090 KT, GUSTS 110 KT
…
REMARKS:
062100Z POSITION NEAR 13.6S 164.1E.
TROPICAL CYCLONE 18P (DONNA), LOCATED APPROXIMATELY 354 NM
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTHWARD AT 02
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY INDICATES 18P IS ENTERING ANOTHER RELATIVE
CONVECTIVE LULL IN ITS CONTINUED PATTERN OF PULSATING DEEP
CONVECTION OBSERVED OVER THE PAST SEVERAL DAYS. BANDING REMAINS
TIGHTLY WRAPPED INTO AN ILL-DEFINED LOW LEVEL CIRCULATION CENTER,
AND A LARGE CONVECTIVE ASYMMETRY HAS FORMED TO THE SOUTHEAST. A
061624Z SSMIS 91 GHZ IMAGE REVEALS THE INTENSE CONVECTION ASSOCIATED
WITH THE CENTRAL BANDING, AND THE 37 GHZ CHANNEL PRESENTS A WELL
DEFINED MICROWAVE EYE. THE INITIAL POSITION IS EXTRAPOLATED FROM THE
AFOREMENTIONED MICROWAVE EYE. A RE-ANALYSIS OF RECENT MICROWAVE
IMAGERY, INCLUDING A 061114Z BYU ASCAT PRODUCT AND ASSOCIATED
NORMALIZED RADAR CROSS SECTION INDICATES DONNA HAS REMAINED ALMOST
QUASI-STATIONARY (QS) FOR NEARLY 18 HOURS. THE CURRENT INTENSITY IS
ASSESSED AT 90 KNOTS BASED ON DVORAK ESTIMATES OF T5.0 FROM PGTW AND
KNES. TC 18P IS CURRENTLY LOCATED WITHIN A COMPETING STEERING
ENVIRONMENT BETWEEN A WEAK SUBTROPICAL RIDGE (STR) OVER NORTHEAST
AUSTRALIA AND A STRONG STR TO THE EAST. GLOBAL MODEL ANALYSES ARE
STARTING TO SUGGEST THE WESTERN STR IS FINALLY STARTING TO ERODE,
WITH THE EASTERN STR EXPECTED TO BECOME THE DOMINANT STEERING
INFLUENCE OVER THE NEXT DAY RESULTING IN A MORE PRONOUNCED SOUTHWARD
MOTION. UPWELLING DURING THIS QS PERIOD HAS LIKELY TEMPERED THE
POTENTIAL FOR INTENSIFICATION. ADDITIONALLY, ALTHOUGH VERTICAL WIND
SHEAR (VWS) IS RELATIVELY LIGHT, THE BROAD AND DIFFUSE UPPER LEVEL
WINDS OVER THE CENTER HAVE NEGATIVELY IMPACTED THE ORGANIZATION OF
THE CENTRAL CORE. AS TC DONNA BEGINS TO MOVE TO THE SOUTH OVER
WARMER WATERS, CONTINUED ROBUST OUTFLOW MAY ALLOW SOME ADDITIONAL
INTENSIFICATION, WITH THE UPPER END OF THE GUIDANCE AROUND 105
KNOTS. THE SYSTEM WILL ACCELERATE AND TURN SOUTHEASTWARD AROUND TAU
48. EXTRA-TROPICAL TRANSITION WILL BEGIN AROUND TAU 72 AS TC DONNA
MOVES OVER COOLER WATERS AND BEGINS TO INTERACT WITH THE BAROCLINIC
ZONE. A SIGNIFICANT INCREASE IN VWS AT THAT TIME WILL INITIATE RAPID
WEAKENING. DONNA IS EXPECTED TO COMPLETE EXTRA-TROPICAL TRANSITION
AND BE FULLY EMBEDDED WITHIN THE MID-LATITUDE WESTERLIES BY TAU 96.
DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT, THEREFORE, THERE IS
HIGH CONFIDENCE IN THE JTWC TRACK FORECAST. MAXIMUM SIGNIFICANT WAVE
HEIGHT AT 061800Z IS 27 FEET. NEXT WARNINGS AT 070300Z, 070900Z,
071500Z, AND 072100Z.

[Manukau heads obs]

it looks like its intensified more in the last few hours

[Nev]

Convection has weakened a little today, revealing spiral banding wrapping around a visible 90 km/h wide ragged eye. Nadi has Donna's central pressure back up to 965 hPa and means-winds down to 160 km/h. JTWC has also reduced winds a little, but, unlike Nadi, still expect some reintensification, before peaking tomorrow…

TROPICAL DISTURBANCE ADVISORY NUMBER A17 ISSUED FROM RSMC NADI
May 070152 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 965HPA WAS LOCATED NEAR 13.9S
164.1E AT 070000 UTC. POSITION POOR BASED ON HR HIMAWARI-8 VIS AND
EIR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTH
SOUTHEAST AT ABOUT 03 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE
CENTRE ESTIMATED AT ABOUT 80 KNOTS.

CONVECTIVE CLOUD BANDS WRAPPING INTO LLCC WITH RAGGED EYE
DISCERNABLE. ORGANIZATION REMAINS GOOD. SYSTEM LIES UNDER AN UPPER
RIDGE IN LOW TO MODERATE SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 29 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON OW EYE WITH LG SURROUND YIELDS DT=5.0, MET
AND PT AGREE. FT BASED ON DT. THUS YIELDING, T5.0/5.0/S0.0/24HRS.

FORECASTS :
AT 12 HRS VALID AT 071200 UTC 15.2S 164.2E MOV S AT 06 KT WITH 75 KT
CLOSE TO CENTRE
AT 24 HRS VALID AT 080000 UTC 16.6S 164.3E MOV S AT 07 KT WITH 70 KT
CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 081200 UTC 17.8S 164.7E MOV S AT 07 KT WITH 70 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 090000 UTC 19.0S 165.3E MOV SSE AT 07 KT WITH 65
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 070800 UTC.

WTPS31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 014//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 014
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
070000Z --- NEAR 13.8S 164.1E
MOVEMENT PAST SIX HOURS - 180 DEGREES AT 04 KTS
POSITION ACCURATE TO WITHIN 060 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 085 KT, GUSTS 105 KT
…
REMARKS:
070300Z POSITION NEAR 14.1S 164.1E.
TROPICAL CYCLONE 18P (DONNA), LOCATED APPROXIMATELY 337 NM
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTHWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) INDICATES A RAGGED EYE IS TRYING TO FORM AS SPIRAL
BANDING WRAPS INTO A LOW LEVEL CIRCULATION CENTER (LLCC), HOWEVER,
CLOUD TOPS HAVE BEEN WARMING. A 062220Z AMSU 89 GHZ IMAGE REVEALS
THE PRIMARY SPIRAL BAND IS WRAPPING AROUND A 50 NM DIAMETER
MICROWAVE EYE. THE INITIAL POSITION IS EXTRAPOLATED FROM THE
AFOREMENTIONED MICROWAVE EYE AND THE PGTW FIX. THE CURRENT INTENSITY
WAS REDUCED SLIGHTLY TO 85 KNOTS BASED ON A RANGE OF DVORAK
ESTIMATES FROM T4.5-5.0 (77 TO 90 KNOTS) FROM PGTW AND KNES,
RELECTING THE SLIGHTLY WEAKENED CONVECTION. TC 18P IS CURRENTLY
LOCATED WITHIN A COMPETING STEERING ENVIRONMENT BETWEEN A WEAK
SUBTROPICAL RIDGE (STR) OVER NORTHEAST AUSTRALIA AND A STRONG STR TO
THE EAST. GLOBAL MODEL ANALYSES SUGGEST THE EASTERN STR SHOULD
BECOME THE DOMINANT STEERING INFLUENCE OVER THE NEXT DAY, RESULTING
IN A MORE PRONOUCED SOUTHWARD MOTION. UPWELLING HAS LIKELY TEMPERED
THE POTENTIAL FOR INTENSIFICATION DUE TO VERY SLOW MOTION OVER THE
PAST 24 HOURS. VERTICAL WIND SHEAR (VWS) IS RELATIVELY LIGHT,
HOWEVER, THE BROAD AND DIFFUSE UPPER LEVEL WINDS OVER THE CENTER
HAVE HAMPERED THE ORGANIZATION OF THE CENTRAL CORE. AS TC DONNA
BEGINS TO MOVE TO THE SOUTH OVER WARMER WATERS, CONTINUED ROBUST
OUTFLOW MAY ALLOW SOME ADDITIONAL INTENSIFICATION OVER THE NEXT 24
HOURS, WITH THE UPPER END OF THE GUIDANCE AROUND 105 KNOTS. THE
SYSTEM WILL ACCELERATE AND TURN SOUTHEASTWARD AROUND TAU 36. EXTRA-
TROPICAL TRANSITION WILL BEGIN NEAR TAU 48 AS TC DONNA MOVES OVER
COOLER WATERS AND BEGINS TO INTERACT WITH THE BAROCLINIC ZONE. A
SIGNIFICANT INCREASE IN VWS AT TAU 72 WILL INITIATE RAPID WEAKENING.
DONNA IS EXPECTED TO COMPLETE EXTRA-TROPICAL TRANSITION AND BE FULLY
EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES BY TAU 96. DYNAMIC MODEL
GUIDANCE IS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE
IN THE JTWC TRACK FORECAST. MAXIMUM SIGNIFICANT WAVE HEIGHT AT
070000Z IS 24 FEET. NEXT WARNINGS AT 070900Z, 071500Z, 072100Z AND
080300Z.

[Nev]

Nice visible 30 km wide ragged eye this afternoon. Donna's finally picking up speed now as she begins her poleward track, after spending the last 24 hours or so stuck around the NW of Vanuatu.
Convection a little weaker and erratic today. Nadi now has her centre up to 970 hPa, with means-winds down to 140 km/h. Be interesting to see how she fares tonight…

TROPICAL DISTURBANCE ADVISORY NUMBER A18 ISSUED FROM RSMC NADI
May 070810 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 970HPA WAS LOCATED NEAR 14.6S
164.6E AT 070600 UTC. POSITION POOR BASED ON HR HIMAWARI-8 VIS AND
EIR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 04 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 75 KNOTS.

CONVECTIVE CLOUD BANDS WRAPPING INTO LLCC WITH RAGGED EYE
DISCERNABLE. ORGANIZATION REMAINS GOOD. SYSTEM LIES UNDER AN UPPER
RIDGE IN LOW TO MODERATE SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 29 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON OW EYE WITH MG SURROUND YIELDS DT=4.5, MET
AND PT AGREE. FT BASED ON DT. THUS YIELDING, T4.5/5.0/W0.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 071800 UTC 15.9S 164.7E MOV S AT 07 KT WITH 75 KT
CLOSE TO CENTRE
AT 24 HRS VALID AT 080600 UTC 16.6S 165.0E MOV S AT 07 KT WITH 75 KT
CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 081800 UTC 18.5S 165.5E MOV SSE AT 07 KT WITH 70
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 090600 UTC 19.7S 166.1E MOV SSE AT 07 KT WITH 70
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 071400 UTC.

WTPS31 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 015//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 015
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
070600Z --- NEAR 14.6S 164.6E
MOVEMENT PAST SIX HOURS - 150 DEGREES AT 08 KTS
POSITION ACCURATE TO WITHIN 015 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 085 KT, GUSTS 105 KT
...
REMARKS:
070900Z POSITION NEAR 15.0S 164.7E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 283 NM
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTH-SOUTHEASTWARD
AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY DEPICTS IMPROVED CONVECTIVE ORGANIZATION WITH A 17-
NM EYE EVIDENT, HOWEVER, DEEP CONVECTION CONTINUES TO CYCLE RAPIDLY.
A 070500Z SSMIS 91 GHZ IMAGE SHOWS ASYMMETRIC CORE CONVECTION WITH A
DEEP CONVECTIVE BAND OVER THE WESTERN SEMI-CIRCLE AND SHALLOW
BANDING OVER THE EASTERN SEMI-CIRCLE OF THE EYEWALL. UPPER-LEVEL
ANALYSIS INDICATES CYCLONIC FLOW OVER THE CORE, WHICH IS LIKELY
CONTRIBUTING TO THE FLAT TREND AND PULSATING CONVECTION, DIVERGING
INTO A STRONG POLEWARD OUTFLOW CHANNEL TO THE SOUTHWEST. THE CURRENT
INTENSITY REMAINS ASSESSED AT 85 KNOTS BASED ON AN AVERAGE OF
4.5/5.0 DVORAK ESTIMATES FROM PGTW, KNES AND PHFO. CURRENT MODEL
ANALYSES INDICATE THAT THE WESTERN SUBTROPICAL RIDGE (STR) HAS
ERODED DUE TO AN APPROACHING MAJOR SHORTWAVE TROUGH, THEREFORE, THE
EASTERN STR IS NOW THE DOMINANT STEERING RIDGE. CONSEQUENTLY, TC 18P
HAS ACCELERATED SOUTHWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY
OF THE STR. TC DONNA SHOULD CONTINUE TO TRACK SOUTHWARD TO SOUTH-
SOUTHEASTWARD THROUGH THE FORECAST PERIOD. DYNAMIC GUIDANCE REMAINS
IN TIGHT AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST
TRACK. TC 18P IS FORECAST TO INTENSIFY SLIGHTLY WITHIN THE NEXT 24
HOURS DUE TO WARM SST AND ROBUST POLEWARD OUTFLOW WITH SOME
UNCERTAINTY DUE TO THE COMPLEX UPPER-LEVEL FLOW OVER THE CORE. AFTER
TAU 24, GRADUAL WEAKENING SHOULD OCCUR AS THE SYSTEM TRACKS OVER
MARGINAL SST. BY TAU 48, TC 18P WILL BEGIN EXTRA-TROPICAL TRANSITION
AND RAPIDLY WEAKEN AS IT INTERACTS WITH THE MIDLATITUDE WESTERLIES
AND THE WEAK BAROCLINIC ZONE. THE SYSTEM IS EXPECTED TO COMPLETE
EXTRA-TROPICAL TRANSITION AS IT BECOMES EMBEDDED WITHIN THE
MIDLATITUDE WESTERLIES. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 070600Z
IS 24 FEET. NEXT WARNINGS AT 071500Z, 072100Z, 080300Z AND 080900Z.//

[Nev]

Donna looks to have strengthened quite a bit overnight, with increased convection and a 40 km wide eye. As per their previous forecast, JTWC increased Donna's mean-winds considerably earlier this morning, whereas Nadi has maintained its status quo…

TROPICAL DISTURBANCE ADVISORY NUMBER A19 ISSUED FROM RSMC NADI
May 071354 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 970HPA WAS LOCATED NEAR 15.4S
164.8E AT 071200 UTC. POSITION POOR BASED ON HR HIMAWARI-8 VIS AND
EIR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 05 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 75 KNOTS.

CONVECTIVE CLOUD BANDS WRAPPING INTO LLCC WITH RAGGED EYE
DISCERNABLE. ORGANIZATION REMAINS GOOD. SYSTEM LIES UNDER AN UPPER
RIDGE IN LOW TO MODERATE SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 29 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON OW EYE WITH MG SURROUND YIELDS DT=4.5, MET
AND PT AGREE. FT BASED ON DT. THUS YIELDING, T4.5/5.0/W0.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 080000 UTC 16.9S 165.1E MOV S AT 08 KT WITH 75 KT
CLOSE TO CENTRE
AT 24 HRS VALID AT 081200 UTC 18.4S 165.6E MOV SSE AT 08 KT WITH 75
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 09000 UTC 19.8S 166.4E MOV SSE AT 08 KT WITH 70 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 091200 UTC 21.3S 167.4E MOV SSE AT 08 KT WITH 65
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 072000 UTC.

WTPS31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 016//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 016
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
071200Z --- NEAR 15.5S 164.8E
MOVEMENT PAST SIX HOURS - 170 DEGREES AT 09 KTS
POSITION ACCURATE TO WITHIN 020 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 095 KT, GUSTS 115 KT
...
REMARKS:
071500Z POSITION NEAR 15.9S 164.8E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 241 NM WEST-
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTHWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS STRENGTHENING, ASYMMETRIC EYEWALL CONVECTION
SURROUNDING A 21-NM EYE. A 071052Z METOP-A 89 GHZ IMAGE SHOWS DEEP
CONVECTION PRIMARILY OVER THE WESTERN SEMI-CIRCLE AND SHALLOW
CONVECTION OVER THE EASTERN SEMI-CIRCLE. UPPER-LEVEL ANALYSIS
INDICATES CYCLONIC FLOW OVER THE SYSTEM, WHICH IS LIKELY
CONTRIBUTING TO THE PULSATING, ASYMMETRIC CORE CONVECTION, DIVERGING
INTO A STRONG POLEWARD OUTFLOW CHANNEL TO THE SOUTHWEST. THE CURRENT
INTENSITY IS ASSESSED AT 95 KNOTS BASED ON AN AVERAGE OF DVORAK
ESTIMATES RANGING FROM T5.0 TO T5.5. CURRENT MODEL ANALYSES INDICATE
THAT THE WESTERN SUBTROPICAL RIDGE (STR) HAS ERODED DUE TO AN
APPROACHING MAJOR SHORTWAVE TROUGH, THEREFORE, THE EASTERN STR IS
NOW THE DOMINANT STEERING RIDGE. CONSEQUENTLY, TC 18P HAS
ACCELERATED SOUTHWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY
OF THE DOMINANT STR. TC DONNA SHOULD CONTINUE TO TRACK SOUTHWARD TO
SOUTH-SOUTHEASTWARD THROUGH THE FORECAST PERIOD. DYNAMIC GUIDANCE
REMAINS IN GOOD AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC
FORECAST TRACK. TC 18P IS FORECAST TO INTENSIFY SLIGHTLY WITHIN THE
NEXT 12 HOURS DUE TO WARM SST AND ROBUST POLEWARD OUTFLOW WITH SOME
UNCERTAINTY DUE TO THE COMPLEX UPPER-LEVEL FLOW OVER THE CORE. AFTER
TAU 12, GRADUAL WEAKENING SHOULD OCCUR AS THE SYSTEM TRACKS OVER
MARGINAL SST. BY TAU 36, TC 18P WILL BEGIN EXTRA-TROPICAL TRANSITION
AND RAPIDLY WEAKEN AS IT INTERACTS WITH THE MIDLATITUDE WESTERLIES
AND THE WEAK BAROCLINIC ZONE. THE SYSTEM IS EXPECTED TO COMPLETE
EXTRA-TROPICAL TRANSITION AS IT BECOMES EMBEDDED WITHIN THE
MIDLATITUDE WESTERLIES. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 071200Z
IS 27 FEET. NEXT WARNINGS AT 072100Z, 080300Z, 080900Z AND 081500Z.//

[Nev]

Whoa! RSMC Nadi have just upgraded Donna back up to Cat 4 with a central pressure down to 948 hPa and means winds of 185 km/h... quite a turnaround…

HURRICANE WARNING 035 ISSUED FROM RSMC NADI May 071903 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 948HPA CATEGORY 4 WAS LOCATED NEAR 16.4
SOUTH 164.7 EAST AT 071800 UTC.
POSITION POOR.
REPEAT POSITION 16.4S 164.7E at 071800 UTC.
CYCLONE MOVING SOUTH-SOUTHEAST AT 09 KNOTS.
EXPECT SUSTAINED WINDS OF 100 KNOTS CLOSE TO THE CENTRE.
…

[Manukau heads obs]

I could see it looked stronger yesterday afternoon, and yet the official reports was it was not
seems like the official reports are like 6 hours compared to live reality

not looking good for New Caledonia

you can see the approaching upper trough affecting the outflow on the western side a little bit now

its timing its S exit well to combine with the current tasman low, assuming its stays on a SSE track and maintains the current speed...still some variables yet
(but you could say the door opened to the south because of the approaching tasman low anyway (which has moved the steering high and sub tropical ridge enough to the east)

[Nev]

Snippet from the media this morning…

'Cyclone Donna now tracking south' - SunLive

“WeatherWatch.co.nz is a CNN affiliate and this morning the Severe Weather Team in Atlanta confirmed to us that Donna's winds of 175km/h puts her tied with 1986's Nadu for the strongest May cyclone on record in the Southern Hemisphere.”

Think they mean TC Namu, which never got past Cat 3 on the BoM/Fiji scale…

[Nev]

JTWC have also increased Donna's winds considerably and showing a 45 km wide ragged eye, although looks clouded over on this morning's visible images…

TROPICAL DISTURBANCE ADVISORY NUMBER A20 ISSUED FROM RSMC NADI
May 072001 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 948HPA WAS LOCATED NEAR 16.4S
164.7E AT 071800 UTC. POSITION POOR BASED ON HR HIMAWARI-8 VIS/EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 09 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 100 KNOTS.

DEEP CONVECTION REMAINS PERSISTANT WITH CLOUD TOP COOLING IN PAST 6
HOURS. ORGANIZATION REMAINS GOOD WITH . SYSTEM LIES UNDER AN UPPER
RIDGE IN LOW SHEARED ENVIRONMENT WITH GOOD POLEWARD OUTFLOW. SST
AROUND 27 DEGREES CELCIUS. SYSTEM STEERED SOUTH-SOUTHEAST ALONG THE
PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH. DVORAK ANALYSIS BASED ON
MG EYE WITH W SURROUND YIELDS DT=6.0, MET AND PT AGREE. FT BASED ON
DT. THUS YIELDING, T6.0/6.0/D1.0/24HRS.


FORECASTS :
AT 12 HRS VALID AT 080600 UTC 18.0S 165.1E MOV SSE AT 08 KT WITH 95
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 081800 UTC 19.4S 165.8E MOV SSE AT 08 KT WITH 85
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 090600 UTC 20.7S 166.4E MOV SSE AT 08 KT WITH 70
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 091800 UTC 22.0S 167.2E MOV SSE AT 08 KT WITH 60
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 080200 UTC.

WTPS31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 017//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 017
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
071800Z --- NEAR 16.5S 164.8E
MOVEMENT PAST SIX HOURS - 180 DEGREES AT 10 KTS
POSITION ACCURATE TO WITHIN 030 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
…
REMARKS:
072100Z POSITION NEAR 16.9S 164.9E.
TROPICAL CYCLONE 18P (DONNA), LOCATED APPROXIMATELY 213 NM WEST-
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTHWARD AT 10
KNOTS OVER THE PAST SIX HOURS. AFTER DAYS OF SLOW OR STALLED
DEVELOPMENT, ANIMATED ENHANCED INFRARED SATELLITE IMAGERY INDICATES
TC 18P HAS IMPROVED ITS OVERALL CONVECTIVE ORGANIZATION AND
MAINTAINED A RAGGED 25 NM DIAMETER EYE DURING A PERIOD OF PRONOUNCED
INTENSIFICATION. THE INITIAL POSITION IS BASED ON EYE FIXES WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 115 KNOTS
BASED ON DVORAK INTENSITY ESTIMATES OF T6.0 (115 KNOTS) FROM KNES
AND NFFN. THE PGTW DVORAK ESTIMATE IS T6.5, HOWEVER, AN ASSESSMENT
OF RECENT 89 GHZ MICROWAVE IMAGERY DOES NOT SUPPORT THAT RANGE AT
THIS TIME. TC DONNA IS CURRENTLY TRACKING SOUTH-SOUTHEASTWARD UNDER
THE INFLUENCE OF A WELL-ESTABLISHED SUB-TROPICAL RIDGE TO THE EAST.
THIS MOTION IS EXPECTED TO CONTINUE OVER THE NEXT 36 HOURS BEFORE
BECOMING MORE SOUTHEASTWARD LATER IN THE FORECAST PERIOD IN RESPONSE
TO AN APPROACHING SHORTWAVE TROUGH. DYNAMIC GUIDANCE REMAINS IN GOOD
AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.
ENVIRONMENTAL CONDITIONS, INCLUDING LIGHT VERTICAL WIND SHEAR (VWS),
ROBUST POLEWARD OUTFLOW, AND WARM SST WATERS WILL PERSIST OVER THE
NEXT 12 HOURS ALLOWING THE SYSTEM TO REMAIN NEAR ITS CURRENT
INTENSITY. BETWEEN TAUS 24 TO 36, SSTS WILL BEGIN TO FALL AND LAND
INTERACTION WITH NEW CALEDONIA WILL INCREASE, INITIATING A SLOW
DISSIPATION. BY TAU 36, TC 18P WILL BEGIN EXTRA-TROPICAL TRANSITION
AND RAPIDLY WEAKEN AS IT MOVES OVER SUB-26 DEGREE CELSIUS WATER AND
INTERACTS WITH MIDLATITUDE WESTERLIES AND THE WEAK BAROCLINIC ZONE.
THE SYSTEM IS EXPECTED TO COMPLETE EXTRA-TROPICAL TRANSITION AT THE
END OF THE FORECAST AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE
WESTERLIES. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 071800Z IS 32 FEET.
NEXT WARNINGS AT 080300Z, 080900Z, 081500Z AND 082100Z.

[Razor]

Category 5 now, according to NZ Herald reports?

[Manukau heads obs]

looking much stronger now, check out this sat image
http://www.goes.noaa.gov/sohemi/sohemil ... irgms.html

seems that moving over fresh water helped?

[Nev]

Yep, RSMC upgraded Donna to Cat 5 at around 1pm today. Central pressure 937 hPa with mean winds around 205 km/h…

TROPICAL DISTURBANCE ADVISORY NUMBER A21 ISSUED FROM RSMC NADI
May 080209 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 937HPA WAS LOCATED NEAR 17.0S
164.8E AT 080000 UTC. POSITION GOOD BASED ON HR HIMAWARI-8 VIS/EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 8 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR
THE CENTRE ESTIMATED AT ABOUT 110 KNOTS.

DEEP CONVECTION REMAINS PERSISTANT WITH CLOUD TOP COOLING.
ORGANIZATION REMAINS GOOD WITH EYE CLEARLY DEFINED. SYSTEM LIES
UNDER AN UPPER RIDGE IN LOW SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 27 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON DG EYE WITH W SURROUND/RING YIELDS DT=6.5,
MET AND PT AGREE. FT BASED ON DT. THUS YIELDING, T6.5/6.5/D1.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 081200 UTC 18.6S 165.4E MOV SSE AT 08 KT WITH 110
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 090000 UTC 20.0S 166.0E MOV SSE AT 08 KT WITH 110
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 091200 UTC 21.4S 166.7E MOV SSE AT 08 KT WITH 95
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 100000 UTC 23.0S 167.7E MOV SSE AT 08 KT WITH 80
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 080800 UTC.

[Nev]

JTWC still only have Donna as the equivalent of a Cat 4 on the Australian and Fiji TC Scale this afternoon, i.e. their 1-minute mean-winds of 115 knots (213 km/h) when converted to 10-minute mean-winds is only about 101 knots (187 km/h). Cat 5 on the Aus/Fiji scale is 10-minute mean-winds of 107 knots (198 km/h) or more…

WTPS31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 018//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 018
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
080000Z --- NEAR 16.9S 164.8E
MOVEMENT PAST SIX HOURS - 180 DEGREES AT 04 KTS
POSITION ACCURATE TO WITHIN 030 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
…
REMARKS:
080300Z POSITION NEAR 17.2S 164.9E.
TROPICAL CYCLONE 18P (DONNA), LOCATED APPROXIMATELY 206 NM WEST-
NORTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTHWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS TIGHTLY CURVED BANDING WRAPPING INTO A WELL
DEFINED AND SYMMETRIC 30 NM EYE, WITH A LARGE CONVECTIVE ASYMMETRY
IN THE SOUTHEAST QUADRANT. THE INITIAL POSITION IS BASED ON EYE
FIXES WITH HIGH CONFIDENCE. A 072254Z AMSU 89 GHZ IMAGE REVEALS A
SOLID CORE OF DEEP CONVECTION COMPLETELY SURROUNDING THE EYE. THE
INITIAL INTENSITY IS ASSESSED AT 115 KNOTS BASED ON DVORAK INTENSITY
ESTIMATES OF T6.0 (115 KNOTS) FROM PGTW, ABRF, AND PHFO, AND IS
SUPPORTED BY CIMSS SATCON. TC DONNA IS CURRENTLY TRACKING UNDER THE
STEERING INFLUENCE OF A WELL-ESTABLISHED SUB-TROPICAL RIDGE TO THE
EAST, WITH MOTION EXPECTED TO BECOME SOUTH-SOUTHEASTERLY TO
SOUTHEASTERLY AS THE STR RE-ORIENTS IN RESPONSE TO AN APPROACHING
SHORTWAVE TROUGH. THE MULTI-MODEL CONSENSUS MEMBERS REMAIN IN MOSTLY
GOOD AGREEMENT AND ENSEMBLE MODEL SPREAD IS GENERALLY LOW, LENDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. ENVIRONMENTAL
CONDITIONS, INCLUDING LIGHT VERTICAL WIND SHEAR (VWS), ROBUST
POLEWARD OUTFLOW, AND WARM SST WATERS WILL PERSIST OVER THE NEXT 12
HOURS ALLOWING THE SYSTEM TO REMAIN NEAR ITS CURRENT INTENSITY.
BETWEEN TAUS 24 TO 36, SSTS WILL BEGIN TO FALL AND LAND INTERACTION
WITH NEW CALEDONIA WILL INCREASE, INITIATING A SLOW DISSIPATION. BY
TAU 36, TC 18P WILL BEGIN EXTRA-TROPICAL TRANSITION AND RAPIDLY
WEAKEN AS IT MOVES OVER SUB-26 DEGREE CELSIUS WATER AND INTERACTS
WITH MIDLATITUDE WESTERLIES AND THE WEAK BAROCLINIC ZONE. THE SYSTEM
IS EXPECTED TO COMPLETE EXTRA-TROPICAL TRANSITION AT THE END OF THE
FORECAST AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 080000Z IS 27 FEET. NEXT WARNINGS
AT 080900Z, 081500Z, 082100Z, AND 090300Z.

[Manukau heads obs]

Its looking amazing on the sat image now
who would have thought a Cat 5 (Fiji scale) in May

[Nev]

JTWC mention that 1-minute mean-winds 'peaked earlier near 120 knots', which converted to 10-minute mean-winds of about 107 knots would have put Donna just on Cat 5 on the Aus/Fiji scale.

Appears to be weakening slightly, with her eye becoming cloud filled this evening. Nadi still has her mean winds around 205 km/h and just a slight pressure drop to 935 hPa.

TROPICAL DISTURBANCE ADVISORY NUMBER A22 ISSUED FROM RSMC NADI
May 080736 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 935HPA WAS LOCATED NEAR 17.3S
164.9E AT 080600 UTC. POSITION GOOD BASED ON HR HIMAWARI-8 VIS/EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 05 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 110 KNOTS.

DEEP CONVECTION REMAINS PERSISTANT WITH CLOUD TOP COOLING.
ORGANIZATION REMAINS GOOD WITH EYE CLEARLY DEFINED. SYSTEM LIES
UNDER AN UPPER RIDGE IN LOW SHEARED ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW. SST AROUND 27 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON OW EYE WITH W SURROUND/RING YIELDS DT=6.5,
MET AND PT AGREE. FT BASED ON DT. THUS YIELDING, T6.5/6.5/D1.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 081800 UTC 18.5S 165.5E MOV SSE AT 07 KT WITH 110
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 090600 UTC 19.7S 166.2E MOV SSE AT 07 KT WITH 110
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 091800 UTC 21.1S 167.0E MOV SSE AT 07 KT WITH 95
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 100600 UTC 22.5S 167.8E MOV SSE AT 07 KT WITH 80
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 081400 UTC.

WTPS31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 019
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
080600Z --- NEAR 17.5S 165.1E
MOVEMENT PAST SIX HOURS - 155 DEGREES AT 07 KTS
POSITION ACCURATE TO WITHIN 020 NM
POSITION BASED ON EYE FIXED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
…
REMARKS:
080900Z POSITION NEAR 17.8S 165.3E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 183 NM WEST
OF PORT VILA, VANUATU, HAS TRACKED SOUTH-SOUTHEASTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. AFTER A PERIOD OF RAPID INTENSIFICATION, TC
18P APPEARS TO BE WEAKENING SLIGHTLY WITH THE EYE BECOMING CLOUD-
FILLED AND CORE CONVECTION INCREASINGLY ASYMMETRIC. A 080446Z SSMIS
91 GHZ IMAGE INDICATES EROSION OF EYEWALL CONVECTION OVER THE WEST
QUADRANT WITH THE BULK OF DEEP CONVECTION NOW OVER THE SOUTHERN SEMI-
CIRCLE. TC 18P PEAKED EARLIER NEAR 120 KNOTS BUT IS NOW ASSESSED AT
115 KNOTS BASED ON THE LOWER END OF DVORAK ESTIMATES RANGING FROM
115 TO 127 KNOTS (T6.0 TO 6.5), CONSISTENT WITH THE CONVECTIVE
STRUCTURE. TC 18P IS FORECAST TO TRACK SOUTH-SOUTHEASTWARD THROUGH
THE FORECAST PERIOD ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH
ORIENTED SUBTROPICAL RIDGE. DYNAMIC GUIDANCE REMAINS IN GOOD
AGREEMENT LENDING HIGH CONFIDENCE TO THE FORECAST TRACK. TC DONNA IS
EXPECTED TO WEAKEN GRADUALLY AS IT TRACKS EAST OF NEW CALEDONIA DUE
TO COOLER SST AND LAND INTERACTION. AFTER TAU 24, THE SYSTEM WILL
BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS WITH A MAJOR
SHORTWAVE TROUGH AND BAROCLINIC ZONE. RAPID WEAKENING IS EXPECTED
AFTER TAU 36 DUE TO STRONG VERTICAL WIND SHEAR AND COLD SST. TC 18P
SHOULD COMPLETE ETT BY TAU 60. MAXIMUM SIGNIFICANT WAVE HEIGHT AT
080600Z IS 27 FEET. NEXT WARNINGS AT 081500Z, 082100Z, 090300Z AND
090900Z.//

[Nev]

Good convection, but Donna looks to have weakened a little more overnight and JTWC have her winds down to around the equivalent of a mid-Cat 4, whereas Nadi still had her at Cat 5 earlier this morning. New Caledonia's eastern Loyalty Islands still look on track to take a direct hit from later today…

TROPICAL DISTURBANCE ADVISORY NUMBER A23 ISSUED FROM RSMC NADI
May 081323 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 935HPA WAS LOCATED NEAR 18.1S
165.5E AT 081200 UTC. POSITION GOOD BASED ON HR HIMAWARI-8 EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING
SOUTH-SOUTHEAST AT ABOUT 07 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 110 KNOTS.

EYE BECOMING CLOUD FILLED BUT STILL DISCERNABLE. DEEP CONVECTION
REMAINS PERSISTANT WITH CLOUD TOP COOLING. ORGANIZATION REMAINS GOOD.
SYSTEM LIES UNDER AN UPPER RIDGE IN LOW SHEARED ENVIRONMENT WITH GOOD
POLEWARD OUTFLOW. SST AROUND 27 DEGREES CELCIUS. SYSTEM STEERED
SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID LEVEL SUBTROPICAL HIGH.
DVORAK ANALYSIS BASED ON LG EYE WITH W SURROUND/RING YIELDS DT=6.0,
MET AND PT AGREE. FT BASED ON DT. THUS YIELDING, T6.0/6.5/D1.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 090000 UTC 19.3S 166.2E MOV SSE AT 07 KT WITH 110
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 091200 UTC 20.6S 167.0E MOV SSE AT 07 KT WITH 100
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 100000 UTC 22.1S 167.8E MOV SSE AT 07 KT WITH 90
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 101200 UTC 24.0S 169.1E MOV SSE AT 07 KT WITH 80
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 082000 UTC.

WTPS31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 020
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
081200Z --- NEAR 18.0S 165.7E
MOVEMENT PAST SIX HOURS - 130 DEGREES AT 08 KTS
POSITION ACCURATE TO WITHIN 040 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 105 KT, GUSTS 130 KT
...
REMARKS:
081500Z POSITION NEAR 18.3S 165.9E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 150 NM WEST
OF PORT VILA, VANUATU, HAS TRACKED SOUTHEASTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS THAT TC 18P HAS BEGUN TO WEAKEN SIGNIFICANTLY WITH A MORE
ASYMMETRIC CONVECTIVE STRUCTURE. A 081030Z METOP-A 89 GHZ IMAGE
INDICATES EROSION OF EYEWALL CONVECTION OVER THE WESTERN SEMI-CIRCLE
AND A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER. CONSEQUENTLY,
THE CURRENT INTENSITY IS ASSESSED AT 105 KNOTS BASED ON THE LOWER
END OF DVORAK ESTIMATES RANGING FROM 102 TO 127 KNOTS. TC 18P IS
FORECAST TO TRACK SOUTH-SOUTHEASTWARD THROUGH THE FORECAST PERIOD
ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH ORIENTED SUBTROPICAL
RIDGE. DYNAMIC GUIDANCE REMAINS IN GOOD AGREEMENT LENDING HIGH
CONFIDENCE TO THE FORECAST TRACK. TC DONNA IS EXPECTED TO WEAKEN
FURTHER AS IT TRACKS EAST OF NEW CALEDONIA DUE TO COOLER SST AND
LAND INTERACTION. AFTER TAU 24, THE SYSTEM WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT) AS IT INTERACTS WITH A MAJOR SHORTWAVE TROUGH AND
BAROCLINIC ZONE. RAPID WEAKENING IS EXPECTED AFTER TAU 36 DUE TO
STRONG VERTICAL WIND SHEAR AND COLD SST. TC 18P SHOULD COMPLETE ETT
BY TAU 60. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 081200Z IS 27 FEET.
NEXT WARNINGS AT 082100Z, 090300Z, 090900Z AND 091500Z.//
NNNN

[David]

Interesting long term intensity difference in those track maps - Nadi have it still at Cat 2 when it reaches 30ºS - whereas JTWC only have 35 knots sustained.

[Nev]

Yes, although Nadi's 8am update looks closer to JTWC's 3am one…

Nadi downgraded Donna to a low Cat 4 around 7am this morning.
Central pressure up to 951 hPa, with mean winds around 170 km/h…

TROPICAL DISTURBANCE ADVISORY NUMBER A24 ISSUED FROM RSMC NADI
May 082017 UTC.

SEVERE TROPICAL CYCLONE DONNA CENTRE 951HPA WAS LOCATED NEAR 18.6S
165.7E AT 081800 UTC. POSITION POOR BASED ON HR HIMAWARI-8 EIR
IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTH
SOUTHEAST-SOUTHEAST AT ABOUT 08 KTS. MAXIMUM 10-MINUTE AVERAGE WINDS
NEAR THE CENTRE ESTIMATED AT ABOUT 90 KNOTS.

DEEP CONVECTION REMAINS PERSISTANT WITH CLOUD TOP COOLING.
ORGANIZATION REMAINS GOOD. SYSTEM LIES UNDER AN UPPER RIDGE IN LOW
SHEARED ENVIRONMENT WITH GOOD POLEWARD OUTFLOW. SST AROUND 27 DEGREES
CELCIUS. SYSTEM STEERED SOUTH-SOUTHEAST ALONG THE PERIPHERY OF A MID
LEVEL SUBTROPICAL HIGH. DVORAK ANALYSIS BASED ON EMBEDDED CENTRE WITH
LG SURROUND, YIELDS DT=4.5, MET AND PT AGREE. FT BASED ON MET. THUS
YIELDING, T4.5/5.5/W0.5/24HRS.

FORECASTS :
AT 12 HRS VALID AT 090600 UTC 19.9S 166.4E MOV SSE AT 07 KT WITH 80
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 091800 UTC 21.2S 167.2E MOV SSE AT 08 KT WITH 70
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 100600 UTC 22.9S 168.3E MOV SSE AT 08 KT WITH 55
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 101800 UTC 25.2S 170.0E MOV SSE AT 10 KT WITH 50
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON TROPICAL CYCLONE DONNA WILL
BE ISSUED AROUND 090200 UTC.

[Nev]

JTWC's latest update has Donna down to the equivalent of a Cat 3, as she approaches the Loyalty Islands today. And from around tomorrow night, looking like she will begin extratropical transition….

WTPS31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 18P (DONNA) WARNING NR 021//
RMKS/
1. TROPICAL CYCLONE 18P (DONNA) WARNING NR 021
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
081800Z --- NEAR 18.7S 166.1E
MOVEMENT PAST SIX HOURS - 150 DEGREES AT 08 KTS
POSITION ACCURATE TO WITHIN 040 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 100 KT, GUSTS 125 KT
…
REMARKS:
082100Z POSITION NEAR 19.0S 166.3E.
TROPICAL CYCLONE (TC) 18P (DONNA), LOCATED APPROXIMATELY 139 NM WEST-
SOUTHWEST OF PORT VILA, VANUATU, HAS TRACKED SOUTH-SOUTHEASTWARD
AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY DEPICTS TC 18P WEAKENING WITH ASYMMETRIC
CONVECTIVE BANDING. THE CURRENT INTENSITY IS ASSESSED AT 100 KNOTS
WHICH IS HEDGED ON THE LOWER END OF THE PGTW DVORAK FIX OF T5.5. THE
SYSTEM IS CURRENTLY IN AN AREA OF LOW VERTICAL WIND SHEAR (VWS),
HIGH SEA SURFACE TEMPERATURES (SSTS 27-28C), AND HAS STRONG POLEWARD
OUTFLOW WITH WEAKER EQUATORWARD OUTFLOW. TC 18P IS FORECAST TO TRACK
SOUTH-SOUTHEASTWARD FOR THE DURATION OF THE FORECAST PERIOD UNDER
THE INFLUENCE OF A SUBTROPICAL RIDGE LOCATED TO THE EAST. AS TC
DONNA TRACKS TO THE SOUTH IT WILL MOVE INTO AN AREA OF COOLER SSTS
AND INCREASING VWS ASSOCIATED WITH A STRONG SHORTHWAVE TROUGH THAT
WILL CONTINUE TO ERODE THE CYCLONE. THE INTERACTION WITH THE
TROUGH AND ITS ASSOCIATED BAROCLINIC ZONE WILL CONCURRENTLY CAUSE
THE SYSTEM TO BEGIN EXTRA-TROPICAL TRANSITION WHICH WILL BE
COMPLETED BY THE END OF THE FORECAST PERIOD. THE DYNAMIC GUIDANCE IS
IN GOOD AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST
TRACK. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 081800Z IS 30 FEET. NEXT
WARNINGS AT 090300Z, 090900Z, 091500Z AND 092100Z.//
NNNN