NZ Weather Forum

Florence is now a cat 1 Hurricane, 984 hPa, 65 knots, moving at 5 knots west (8am NZT)
EC and UKM on the 12z runs this morning have locked Hurricane Florence as a major Hurricane impacting North Carolina within 96 to 120 hours. U.S hurricane models are now projecting similar scenarios. Key points for the next 72 hours

 -Sea surface temps ranging from 28 to 30c
 -Very favourable wind shear 5 to 10 knots
 -High chance of rapid intensification before landfall
 -Ridge strengthening to the north
 -Upper level steering winds almost non-existent as she approaches the coast

The last point is a forecasting nightmare and makes Florence very unpredictable as she approaches the mainland. This will most likely be the most watched weather event on the planet for 2018.

Some truly remarkable model runs on the 00z for a U.S landfall. Due to a lack of upper level steering and a strong ridge blocking from the north, Florence is likely to crawl and maybe stall as she reaches the coast, creating an historic and devastating assault on the SE U.S coast. Winds around 120 to 140 knots alongside a widespread 800 to 1100mm + event are projecting on many of the big models.

Climate wise, some of these model projections are not close to normal. Major category 4 hurricane generally never hit North Carolina. The only one that has been recorded (since 1851) is hurricane Hazel in 1954, which hit the South and North Carolina border. Only 4 cat 4 hurricanes have ever crossed higher than Florida. History suggests something is amiss and the infamous right hand turn along the subtropical ridge may come later than models are projecting?

For now, Florence is intensifying with lightning observed around the eyewall and CB 'Hot towers' penetrating the tropopause into the stratosphere. This is a sign that the first stages of rapid intensification is commencing. The strengthening inner eyewall shows no sign of dry air intrusions.

Stalling, probably, making it the most destructive hurricane in America's history according to the media.

GFS output for 00Z Friday.

Using the Advanced Dvorak technique, Florence has dropped 37 hPa in the last 9 hours with sustained winds of 115 knots. Although NHC has yet to upgrade, she has just gone to Cat 4.

Currently hurricane Florence is a Category 4, pressure has stabilised over the last 9 hours @943 hPa, winds are 120 knots (222 km/h), she is travelling WNW at around 16 km/h and has the characteristics of an annular cyclone. No signs of an eyewall replacement cycle at this point, so intensity should be maintained for the next 24 hours.

All models on the 00z run including the high resolution U.S Hurricane model HWRF are putting a bullseye on North Carolina. Intensity on landfall looks likely to be a category 4 and possibly a 5. She is likely to be one of the most devastating hurricanes in U.S recorded history. Storm surge will be extraordinary.... here is a photo from North Carolina of the storm surge level that was reached by the only cat 4 hurricane (Hazel 1954) to have hit the state. Florence will most likely have a higher surge.

An eyewall replacement cycle was complete overnight, expanding the eye to around a 60 km radius. This will expand the wind field and allow further intensification over the next 24 hours. Currently (9pm UTC, 9am NZT 1209) Florence is a Cat 4, 950 hPa, winds 115 knots (213 km/h), moving WNW at 30 km/h. Now an annular cyclone with outflow jets in the NW and eastern quadrants giving her that look of the ‘donut of destruction’.

The EC 12z run this morning has produced a nightmare scenario for the Carolina’s as Florence is stalled by the effect of a nearby mid latitude trough zapping the upper level steering. EC believes that Florence will stall and do an abnormal left turn down the coast and rake both Carolina’s. With EC the only model in the world that takes ocean coupling into its projections, that run needs to be taken seriously.

Looking at the latest microwave imagery, there seems to be a secondary outer eyewall developing on Florence ….. unusual behaviour on the back the last eyewall replacement only 15 hours ago. Massive poleward and equatorward outflows now on Florence as she takes deep breathes. ADT method has her now dropped to 941 hPa, around 120 knot winds.

Currently there are 2 simultaneous major destructive cyclonic gyres spinning in the Northern Hemisphere. Super Typhoon Mangkhut is now a Cat 5 (916 hPa, 140 knots) and nearing the Philippines, potentially heading to Hong Kong in 5 days.

Not looking good for the Carolina's.

Hurricane Olivia in the Pacific is now a tropical storm and about to cross Hawaii.

Florence’s pressure had moved back up to 948 hPa and now back to 945 hPa on the ADT method in the last 2 hours. It seems that an outer eyewall is replacing the recently formed existing one…. This normally means initial weakening before re-intensification with a larger eye.

Model wise – the uncertainty on the behaviour of landfall has increased on the 00Z runs. Georgia and Florida residents will wake up this morning with a rude shock from the EC 00z run. EC has been picking up a 2nd blocking ridge inland which forces an abnormal left turn. This then allows Florence to rake the Carolinas and move back offshore heading towards Georgia and Florida for a 2nd attempted crossing. An alarming twist is unfolding for 4 states if that verifies.

Pressure now down to 939 hPa on the ADT method. Winds 120 knots. Centre has increased temp to 16c. The strongest Florence has been and edging nearer to cat 5.

I grabbed this photo off FB which shows Florence from the Space station, amazing photo i thought

Great Pic Richard. Hard to imagine a better view of the centre.

Another.... eyewall replacement cyclone is occurring, which has weakened Florence to a high end cat 3. During this last ERC, some dry air has penetrated near the core. Hard to see her strengthen much more but the SST's are still around 28c with low shear, so who knows. Cirrus clouds now arriving on the coast. Outer bands will also lift tornado risk as the day goes on.

946 hPa, 110 knots moving at 30 km/h NW.

Model wise - It's very grim for Carolina's and Georgia. The stalling pattern and left turn now picked up by most models as a blocking ridge inland will stop Florence in her tracks. IMO, she could S wobble down the coastline for days

Interesting - overlay of the U.S hurricane ensembles and individual models from the latest 18z run shows Florence's eye further north of their projections on the 9.45am NZT sat pic. Potentially a large S wobble.

Wind shear has increased allowing dry air to penetrate into the inner core, so Florence's south side has become a little unravelled. The inner-core and outer wind fields have expanded though, making storm surge an even larger issue around sea level.

Florence is getting a taste of the mid latitudes with wind shear attempting to rip her to shreds. Maximum winds speeds have dropped to 100 knots, pressure 955 hPa but her wind field size has increased significantly. It's normally what happens when cyclones commence transitioning from Tropical to Extratropical. It will be interesting to see how she handles the next 12 hours...she may lose her 'Major Hurricane' tag i'd say.

U.S radar now picking up near her inner core. Radar showing her last hot tower breaching into the tropopause and lower stratosphere around 60,000 feet.

Several hot towers in the last hour with lightning around the eyewall which normally occurs with re-intensification. She has spat out that dry air. is moving over 28c SST's and starting to re-organise her structure. I fear SE coast American's have been going to bed thinking the beast was done and dusted....

get out the pop corn

Some coastal areas certainly going to take a battering. This forecast below is for Cape Lookout, NC, from Windfinder. Shows 670mm rain in 24 hours

Check out the photos from the space station! https://twitter.com/astro_ricky/status/ ... 8975432704

Florence stabilised overnight but is still having injections of dry air around the inner eyewall. If she can spit this dry air out, she may still intensify a little more as the sea surface temp is near 29c.

Currently Cat 2, 955 hPa, 90 knots, moving WNW at 16 km/h – here is the latest radar and sat imagery.

Early storm surge from a 5 hours ago. Probably double this height by now.

https://twitter.com/i/status/1040253237616619520

Her forward movement has started to slow as the ridge to the west starts to block her passage.

Currently travelling at 8km/h WNW

Another re-intensification underway. Deep wrapping convection evident in the last hour.

Cape Lookout land ob now gusting to 84 knots, sustained 71 knots on the northern edge of the outer eyewall. Must be cranking on that little inner eyewall