Tropical Cyclone Pam - SW Pacific

[David]

Seems to be good consistent model agreement of it passing to the east of NZ now as a low of around 950 hPa.

[Nev]

Yep, GFS probably the closest to NZ, but even that has moved further east on this morn's 12z run…

TROPICAL DISTURBANCE ADVISORY NUMBER A3 ISSUED FROM RSMC NADI
Mar 07/2011 UTC 2015 UTC.

TROPICAL DISTURBANCE 11F CENTRE [1000HPA] WAS LOCATED NEAR 8.4S
169.0E AT 071800 UTC. POSITION POOR BASED ON HR GMS EIR IMAGERY AND
PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTHWEST AT ABOUT 3
KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT
ABOUT 20 KNOTS.

ORGANISATION HAS SLIGHTLY IMPROVED IN THE PAST 24 HOURS. CONVECTION
REMAINS PESISTENT NORTH OF LLCC. SYSTEM LIES UNDER AN UPPER RIDGE IN
A LOW SHEARED ENVIRONMENT. CYCLONIC CIRCULATION EXTENDS TO 500HPA.
SST AROUND 30 DEGREES CELSIUS. DVORAK ANALYSIS BASED ON 0.2 WRAP
YEILDS DT=1.5, MET AND PAT AGREES. THUS YEILDING 1.5/1.5/D0.5/24HRS.

GLOBAL MODELS HAVE PICKED THE SYSTEM AND SLOWLY MOVE IT SOUTHWARDS
WITH FURTHER INTENSIFICATION.

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE IN THE
NEXT 24 TO 48 HOURS TO HIGH.
...

[jamie]

Jeez we are lucky this doesn't look like it will hit NZ. We could be looking at 200km+ winds otherwise. Mind you that would be one fascinating experience.

I hope it spares all the islands.

[Manukau heads obs]

until it actually recurves, nothing is certain about its future path

[Nev]

Totally agree about the uncertainty of this potential TC's future. TC's are notoriously unpredictable and models are a just that, a best-guess (especially this far out), based on current available data.

Having said that, GFS is inclining even further east sparing Vanuatu, as is evident on Nadi's latest track-map. Also looking like sometime tomorrow before TC status...

TROPICAL DISTURBANCE ADVISORY NUMBER A4 ISSUED FROM RSMC NADI
Mar 08/0153 UTC 2015 UTC.

TROPICAL DISTURBANCE 11F CENTRE 1001HPA WAS LOCATED NEAR 8.8S 168.9E
AT 080000 UTC. POSITION POOR BASED ON HR GMS VIS IMAGERY AND
PERIPHERAL SURFACE REPORTS. DISTURBANCE MOVING SOUTH-SOUTHWEST AT
ABOUT 4 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE
ESTIMATED AT ABOUT 20 KNOTS.

ORGANISATION HAS IMPROVED SLIGHTLY PAST 24 HOURS. CONVECTION REMAINS
PESISTENT. SYSTEM LIES UNDER AN UPPER DIFLLUENT REGION IN A LOW
SHEARED ENVIRONMENT. SST AROUND 30 DEGREES CELSIUS. DVORAK ANALYSIS
BASED ON 0.2 WRAP YEILDS DT=1.5, MET AND PAT AGREE. THUS YEILDING
1.5/1.5/D0.5/24HRS.

GLOBAL MODEL HAVE PICKED THE SYSTEM AND MOVE IT SOUTHWARDS WITH
FURTHER INTENSIFICATION.

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE IN THE
NEXT 24 TO 48 HOURS IS HIGH.
...

[David]

Models seem to be shifting it further east almost every update...

[Nev]

Yes, although the departing high is quite weak, so it could still slide down our way. Then again this low may not be quite as strong as first thought.

JTWC don't appear to be overly excited at this stage…

ABPW10 PGTW 080600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE WESTERN AND
/SOUTH PACIFIC OCEANS/080600Z-090600ZMAR2015//
RMKS/
…
2. SOUTH PACIFIC AREA (WEST COAST OF SOUTH AMERICA TO 135 EAST):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 7.8S
169.9E, IS NOW LOCATED NEAR 8.3S 169.3E, APPROXIMATELY 746 NM
NORTHWEST OF NADI, FIJI. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
SHOWS A VERY BROAD, PERSISTENT CONVECTION WITH MONSOON DEPRESSION
CHARACTERISTICS AND FRAGMENTED FORMATIVE BANDS WRAPPING INTO AN ILL-
DEFINED BUT SLOWLY CONSOLIDATING LOW LEVEL CIRCULATION CENTER. UPPER
LEVEL ANALYSIS INDICATES AN OVERALL FAVORABLE ENVIRONMENT WITH LOW
TO MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR OFFSET BY A POINT
SOURCE PROVIDING EXCELLENT OUTFLOW. SEA SURFACE TEMPERATURES IN THE
AREA ARE HIGHLY FAVORABLE AT 30 CELSIUS. MODEL GUIDANCE IS IN GOOD
AGREEMENT WITH A SIGNIFICANT TROPICAL CYCLONE DEVELOPING BEYOND TAU
36. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS.
MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1002 MB. THE
POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.

[Manukau heads obs]

BOM model though has it stiring up a bit of a hornets nest in the southern ocean as it passes just to our east..i.e will cause a pattern change one or the other...
(have seen that sort of thing happen beore)

[Nev]

Yes, in an earlier run GFS had two small TC's following in this ones wake. One forming around Qld's Cape York around March 12 and heading SE into the Coral Sea, and the other forming just west of Fiji around March 19 and heading SW into the South Pacific. The North Qld one still looks viable though…

[Manukau heads obs]

to me, it looks like a mis-fire occured today...latest sat animation sequence shows less rotation ...
but still a large broad area of convection!
also to me its generally drifting west, the overall center of organization, currently...

[Nev]

Interesting… I thought rotation had improved today. But yes, I think it has moved slightly WSW this arvo.

Latest advice from RSMC Nadi…

TROPICAL DISTURBANCE ADVISORY NUMBER A5 ISSUED FROM RSMC NADI
Mar 08/0754 UTC 2015 UTC.

TROPICAL DEPRESSION 11F CENTRE 997HPA WAS LOCATED NEAR 8.0S 169.7E AT
080600 UTC. POSITION POOR BASED ON HR GMS IR/VIS IMAGERY AND
PERIPHERAL SURFACE REPORTS. DEPRESSION SLOW MOVING. MAXIMUM
10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 25 KNOTS.

ORGANISATION HAS IMPROVED SLIGHTLY PAST 24 HOURS. CONVECTION REMAINS
PESISTENT. SYSTEM LIES UNDER AN UPPER DIFFLUENT REGION IN A LOW TO
MODERATE SHEARED ENVIRONMENT. CYCLONIC CIRCULATION EXTENDS TO 500HPA.
SST AROUND 30 DEGREES CELSIUS. DVORAK ANALYSIS BASED ON 0.3 WRAP
YEILDS DT=2.0, PAT AND MET AGREE. THUS YEILDING 2.0/2.0/D0.5/24HRS.

GLOBAL MODEL HAVE PICKED THE SYSTEM AND MOVE IT SOUTHWARDS WITH
FURTHER INTENSIFICATION.

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE WITHIN
THE NEXT 24 TO 48 HOURS IS HIGH.
...

[Manukau heads obs]

Actually i take it back
new blow up now on latest sat image at the general circulation center

[Nev]

Yes, that convection over and around the LLCC has persisted throughout the night.
I'd be surprised if she wasn't named later today…

TROPICAL DISTURBANCE ADVISORY NUMBER A7 ISSUED FROM RSMC NADI
Mar 08/1939 UTC 2015 UTC.

TROPICAL DEPRESSION 11F CENTRE 999HPA WAS LOCATED NEAR 7.9S 168.5E AT
081800 UTC. POSITION POOR BASED ON HR GMS EIR IMAGERY AND PERIPHERAL
SURFACE REPORTS. DEPRESSION MOVING NORTHWEST AT ABOUT 2 KNOTS.
MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 25
KNOTS.

ORGANISATION HAS NOT CHANGED MUCH IN THE PAST 24 HOURS. CONVECTION
REMAINS PESISTENT AROUND SUPPOSED LLCC. SYSTEM LIES UNDER AN UPPER
RIDGE IN A LOW SHEARED ENVIRONMENT. SST AROUND 30 DEGREES CELSIUS.
DVORAK ANALYSIS BASED ON 0.2 WRAP WITH WHITE BAND YEILDS DT=2.0, MET
AND PAT AGREES. THUS YIELDING T2.0/2.0/D0.5/24HRS.

GLOBAL MODEL HAVE PICKED THE SYSTEM AND MOVE IT SOUTHWARDS WITH
FURTHER INTENSIFICATION.

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE WITHIN
THE NEXT 24 HOURS IS HIGH.
...

[Manukau heads obs]

this is a good sat animation here:
http://www.goes.noaa.gov/sohemi/sohemil ... irgms.html

you can see how its slow moving

and this WV animation
http://www.goes.noaa.gov/sohemi/sohemil ... wvgms.html

shows a surge from the SE..cant see it moving SE any time soon?

the latest BOM model has it a bit closer to NZ again...i.e a flip flop...which is what I said would happen with the models...

[Nev]

JTWC have just issued a TC Formation Alert for this low…

WTPS21 PGTW 082300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
200 NM EITHER SIDE OF A LINE FROM 5.6S 168.9E TO 12.9S 171.1E
WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 28 TO 33 KNOTS. METSAT
IMAGERY AT 082100Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 7.7S 169.4E. THE SYSTEM IS MOVING EAST-SOUTHEASTWARD AT 06
KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 8.3S
169.3E, IS NOW LOCATED NEAR 7.7S 169.4E, APPROXIMATELY 770 NM
NORTHWEST OF NADI, FIJI. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY SHOWS AN ELONGATED SIGNATURE WITH DEEPENED CONVECTION
ASSOCIATED WITH A SLOWLY-CONSOLIDATING LOW-LEVEL CIRCULATION CENTER
(LLCC). A 082017Z SSMIS MICROWAVE IMAGE REVEALS THE BULK OF
CONVECTIVE BANDING OVER THE NORTHERN SEMI-CIRCLE BROADLY WRAPPING
INTO THE LLCC. A 081857Z WINDSAT PASS SHOWS A 25 TO 30 KNOT
CIRCULATION WITH STRONGER WINDS UP TO 40 KNOTS WELL NORTH OF THE
SYSTEM. UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY FAVORABLE
ENVIRONMENT WITH MODERATE TO HIGH VERTICAL WIND SHEAR OFFSET BY GOOD
OUTFLOW. ADDITIONALLY, WARM SEA SURFACE TEMPERATURES IN THE
AREA ARE CONDUCIVE FOR DEVELOPMENT. MAXIMUM SUSTAINED SURFACE WINDS
ARE ESTIMATED AT 28 TO 33 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1000 MB. DUE TO PERSISTENT CONVECTION AND
IMPROVED ORGANIZATION, THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS HIGH.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
092300Z.//
NNNN

[Manukau heads obs]

not sure how they come up with these movement ideas...e.g moving ESE at 4 knots
when its not clear the exact position
the sat image animation at 12pm NZ time showed a flare up..but that was on the eastern side of the LLCC
now the 1pm has that as 'gone' and shows the generaly center of circulation as un changed...i.e its basicly stationary at the moment....

[Manukau heads obs]

here is 2 sat images
the coloured one is from 2 days ago..when it was first forming...
the general circulation center is shown

the black and white sat image is the latest...its basicly been slow moving ...and drifted west a bit if anything..

(note the scale is a bit different, i.e the coloured one shows a 5 degree longitude line)

[Manukau heads obs]

http://blog.metservice.com/2015/03/trop ... ate-mar15/

[Nev]

Nice blog.

Still not quite a Cat 1 yet…

TROPICAL DISTURBANCE ADVISORY NUMBER A8 ISSUED FROM RSMC NADI
Mar 09/0136 UTC 2015 UTC.

TROPICAL DEPRESSION 11F CENTRE 997HPA WAS LOCATED NEAR 8.2S 169.4E AT
090000 UTC. POSITION POOR BASED ON HR GMS VIS IMAGERY AND PERIPHERAL
SURFACE REPORTS. DEPRESSION MOVING SOUTH AT ABOUT 02 KNOTS. MAXIMUM
10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 30 KNOTS.

ORGANISATION HAS SLIGHTLY IMPROVED IN THE PAST 24 HOURS. CONVECTION
REMAINS PESISTENT AROUND SUPPOSED LLCC. SYSTEM LIES UNDER AN UPPER
RIDGE IN A LOW SHEARED ENVIRONMENT. SST AROUND 30 DEGREES CELSIUS.
DVORAK ANALYSIS BASED ON 0.4 WRAP WITH WHITE BAND YEILDS DT=2.5, MET
AND PAT AGREES. THUS YIELDING T2.5/2.5/D1.0/24HRS.

GLOBAL MODEL HAVE PICKED THE SYSTEM AND MOVE IT SOUTHWARDS WITH
FURTHER INTENSIFICATION.

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE WITHIN
THE NEXT 24 HOURS IS HIGH.
...

[Manukau heads obs]

DEPRESSION MOVING SOUTH AT ABOUT 02 KNOTS

I dont get how they can say that
2 kts?
you would need to have very accurate location to know it was only moving at 2 kts
and yet

POSITION POOR

why dont they just saying its slow moving?

[Manukau heads obs]

at this site you can access UKmet model
as well as the others

http://meteocentre.com/models/explorate ... est&hh=000

but its only a southern hemisphere model...so its a bit hard on the neck

[Nev]

Hmm… guessing vertical wind shear is culprit for its slow development…

ABPW10 PGTW 090600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE WESTERN AND
/SOUTH PACIFIC OCEANS/090600Z-100600ZMAR2015//
RMKS/
…
2. SOUTH PACIFIC AREA (WEST COAST OF SOUTH AMERICA TO 135 EAST):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 7.7S
169.4E, IS NOW LOCATED NEAR 8.3S 169.6E, APPROXIMATELY 715 NM
NORTHWEST OF NADI, FIJI. RECENT ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS A BROAD AND ELONGATED CIRCULATION WITH DEEP
CONVECTIVE BANDS THAT ARE SLOWLY CONSOLIDATING. UPPER-LEVEL
ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE
TO HIGH (20-30 KNOT) VWS OFFSET BY GOOD EQUATORWARD OUTFLOW.
ADDITIONALLY, WARM SEA SURFACE TEMPERATURES IN THE AREA ARE
CONDUCIVE FOR DEVELOPMENT. MAXIMUM SUSTAINED SURFACE WINDS ARE
ESTIMATED AT 28 TO 33 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF
A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS
HIGH.
…

[Dean.]

I guess the slower it develops the more chance of it clipping NZ...

[Nev]

TC Pam finally named by RSMC Nadi tonight…

TROPICAL DISTURBANCE ADVISORY NUMBER A9 ISSUED FROM RSMC NADI
Mar 09/0752 UTC 2015 UTC.

TROPICAL CYCLONE PAM CENTRE 995HPA CATEGORY 1 WAS LOCATED NEAR 8.4S
169.8E AT 090600 UTC. POSITION POOR BASED ON HR GMS EIR/VIS IMAGERY
AND PERIPHERAL SURFACE REPORTS. DEPRESSION MOVING EAST-SOUTHEAST AT
ABOUT 04 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE
ESTIMATED AT ABOUT 35 KNOTS.
EXPECTS WINDS OVER 33 KNOTS WITHIN 180 NAUTICAL MILES IN NE QUADRANT

AND WITHIN 180 NAUTICAL MILES IN SE QUADRANT

AND WITHIN 120 NAUTICAL MILES IN SW QUADRANT

AND WITHIN 180 NAUTICAL MILES IN NW QUADRANT

ORGANISATION HAS IMPROVED PAST 24 HOURS. PRIMARY BANDS TRYING TO WRAP
AROUND LLCC. CONVECTION REMAINS PESISTENT. SYSTEM LIES UNDER AN UPPER
RIDGE IN A LOW TO MODERATE SHEARED ENVIRONMENT. OUTFLOW GOOD.
CYCLONIC CIRCULATION EXTENDS TO 300HPA. SST AROUND 30 DEGREES
CELSIUS. DVORAK ANALYSIS BASED ON 0.6 WRAP ON VIS YEILDS DT=3.0, MET
AND PAT AGREES. THUS YEILDING 3.0/3.0/D1.0/24HRS.

GLOBAL MODEL HAVE PICKED THE SYSTEM AND MOVE IT SOUTHWARDS WITH
FURTHER INTENSIFICATION.
...

[Nev]

JTWC remarks...

WTPS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 17P (SEVENTEEN) WARNING NR 001//
RMKS/
1. TROPICAL CYCLONE 17P (SEVENTEEN) WARNING NR 001
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
090600Z --- NEAR 8.5S 169.8E
MOVEMENT PAST SIX HOURS - 135 DEGREES AT 03 KTS
POSITION ACCURATE TO WITHIN 025 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
WIND RADII VALID OVER OPEN WATER ONLY
...
REMARKS:
090900Z POSITION NEAR 8.7S 169.9E.
TROPICAL CYCLONE 17P (SEVENTEEN), LOCATED APPROXIMATELY 760 NM
NORTHWEST OF NADI, FIJI, HAS TRACKED SOUTHEASTWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. RECENT ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS AN EXPANSIVE AND ELONGATED SYSTEM WITH FORMATIVE
CONVECTIVE BANDS - MOSTLY FROM THE NORTHERN PERIPHERY - THAT ARE
FEEDING INTO A LARGE AND SLOWLY CONSOLIDATING LOW LEVEL CIRCULATION
CENTER. THE INITIAL POSITION IS BASED ON A LOW REFLECTIVITY NOTCH
FEATURE ON A 090501Z GPM MICROWAVE IMAGE. THE INITIAL INTENSITY IS
BASED ON CONGRUENT DVORAK ESTIMATES FROM PGTW AND PHFO. UPPER-LEVEL
ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE
TO HIGH (20-30 KNOT) VERTICAL WIND SHEAR (VWS) OFFSET BY GOOD
EQUATORWARD OUTFLOW. THE CYCLONE IS CURRENTLY TRACKING SLOWLY ALONG
THE SOUTHERN EDGE OF A SHALLOW NEAR EQUATORIAL RIDGE TO THE NORTH.
AFTER TAU 24, A BUILDING SUBTROPICAL RIDGE TO THE EAST WILL ASSUME
STEERING AND DRIVE THE SYSTEM ON A MORE POLEWARD TRAJECTORY. TC 17P
IS EXPECTED TO STEADILY INTENSIFY AS VWS DECREASES AND OUTFLOW
IMPROVES WITH THE INTRODUCTION OF A POLEWARD OUTFLOW CHANNEL AS THE
CYCLONE TRACKS SOUTHWARD. RAPID INTENSIFICATION IS A DISTINCT
POSSIBILITY TOWARDS TAU 72 AS THE SYSTEM BECOMES EXP0SED TO THE
STRONG WESTERLIES. AFTER TAU 96, TC 17P WILL TRACK MORE SOUTHEASTWARD
AS THE STR IS WEAKENED BY A MID-LATITUDE TROUGH. THE AVAILABLE
NUMERIC GUIDANCE IS IN OVERALL AGREEMENT IN THE LONG TERM, HOWEVER,
THERE IS A SIGNIFICANT SPREAD IN THE INITIAL PORTION OF THE FORECAST
PRIOR TO THE TRANSITION IN THE STEERING MECHANISM. IN VIEW OF THIS
DISCREPANCY, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 090600Z IS 18 FEET. NEXT WARNINGS
AT 092100Z AND 100900Z.//
NNNN