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Tropical Update #2 – September 7, 2018

To All,

The 11:00 am advisory has moved a little south, based on this advisory Hurricane Florence will be about 460 miles from our coast on Wednesday morning.   Still early to tell exactly where Florence will make landfall, but we need to prepare now.


Tropical Storm Florence Discussion Number  33

NWS National Hurricane Center Miami FL       AL062018

1100 AM AST Fri Sep 07 2018

Moderate to strong southwesterly shear continues to affect Florence,

but visible and microwave satellite images indicate that the

cyclone is maintaining a vigorous, but tilted, circulation.

A mid-level eye feature is noted in both types of satellite

imagery, but the low-level center still appears displaced to the

southwest.  Subjective and objective satellite intensity estimates

have stopped falling–and some have even begun to increase a bit

again–so the initial intensity is being held at 55 kt.

The shear over Florence has likely reached its maximum and is

expected to decrease below 20 kt in 6-12 hours and then decrease to

10 kt or less in 36 hours.  All the while, sea surface temperatures

will be gradually increasing to between 28-29C, and perhaps more

importantly, oceanic heat content values will double in 3-4 days.

It may take the cyclone some time to gather itself once the shear

abates, but once it becomes vertically stacked again, the intensity

is likely to increase significantly.  The guidance is in agreement

on this scenario, and Florence is likely to re-attain hurricane

status in about 48 hours and then potentially major hurricane

strength by days 4-5.  The new official forecast is fairly similar

to the previous one, generally close to the ICON intensity consensus

and slightly below the HCCA model on days 4 and 5.

Florence is moving westward, or 270/7 kt, to the south of the

eastern periphery of a subtropical ridge extending east of the

Mid-Atlantic United States.  The global model guidance is actually

in fairly good agreement on the general evolution of the steering

pattern around Florence through day 5.  While it remains a tilted

cyclone, Florence is expected to continue moving westward for the

next 48 hours.  After that time, a break in the ridge should allow

Florence to turn west-northwestward over the southwestern Atlantic.

A new mid-level ridge is expected to develop over the western

Atlantic on days 4-5, but the position of that high will play a big

role regarding how much Florence may turn by the end of the

forecast period.  Only a slight southward nudge of forecast track

was required on this cycle, keeping the NHC prediction between the

GFS and ECMWF solutions.

Key Messages:

1. Regardless of Florence’s eventual track, large swells will begin

to affect Bermuda later today and portions of the U.S. East Coast

this weekend, resulting in life-threatening surf and rip currents.

2. The risk of other direct impacts associated with Florence along

the U.S. East Coast next week has increased.  However, there is

still very large uncertainty in model forecasts of Florence’s track

beyond day 5, making it too soon to determine the exact location,

magnitude, and timing of these impacts.  Interests near and along

the U.S. East Coast should monitor the progress of Florence through

the weekend and ensure they have their hurricane plans in place.


INIT  07/1500Z 25.0N  51.8W   55 KT  65 MPH

12H  08/0000Z 24.9N  52.8W   55 KT  65 MPH

24H  08/1200Z 24.9N  54.0W   55 KT  65 MPH

36H  09/0000Z 24.9N  55.1W   60 KT  70 MPH

48H  09/1200Z 25.1N  56.2W   65 KT  75 MPH

72H  10/1200Z 25.9N  59.8W   90 KT 105 MPH

96H  11/1200Z 27.5N  65.5W  110 KT 125 MPH

120H  12/1200Z 30.0N  72.0W  115 KT 130 MPH


Forecaster Berg

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