Hurricane Dorian Discussion Number 24
NWS National Hurricane Center Miami FL AL052019
500 AM AST Fri Aug 30 2019
There hasn't been a lot of new data since the Hurricane Hunter
planes departed Dorian several hours ago. The convective pattern
on infrared satellite imagery has been nearly steady state,
although the latest Dvorak estimates from TAFB and SAB rose to
T5.0/90 kt. These estimates, combined with the earlier aircraft
data, support maintaining an initial intensity of 90 kt.
Dorian's heading is very gradually turning toward the left, with
the latest estimate northwestward, or 320 degrees at 10 kt. Dorian
is now being steered between a mid-tropospheric high centered near
Bermuda and a mid-/upper-level low located over the Bahamas. The
high is expected to expand westward, with a blocking ridge becoming
established over the western Atlantic during the next several days.
With the exception of COAMPS-TC and HMON, the other reliable models
are in excellent agreement through day 3, with Dorian turning
westward south of the ridge and moving near or over the
northernmost islands in the Bahamas Sunday and Monday. After day
3, steering currents collapse as a break develops in the ridge, and
Dorian will likely slow down considerably as it approaches the
Florida peninsula. There is more spread among the deterministic
models and their ensemble members during that time, with
disagreement on exactly when and where Dorian will turn
northwestward and northward on days 4 and 5. That being said, the
tracks of the simple and corrected consensus models on this cycle
did not warrant much change to the official NHC forecast, with
perhaps just a slight southward adjustment on days 3 and 4. The
biggest concern will be Dorian's slow motion when it is near
Florida, placing some areas of the state at an increasing risk of a
prolonged, drawn-out event of strong winds, dangerous storm surge,
and heavy rainfall.
The upper-level low to the west of Dorian continues to impart some
southwesterly shear over the hurricane, which has prevented it from
strengthening rapidly. However, Dorian is expected to enter a more
favorable upper-level environment during the next 24 hours, which
should allow its structure to become more well developed. Although
overall the environment ahead of the storm appears conducive for
strengthening, some models (in particular the ECMWF) suggest that
some northerly shear could come into play while Dorian moves
through the northwestern Bahamas, and for that reason the NHC
official intensity forecast is not quite as bullish as the HCCA,
Florida State Superensemble, and HWRF models. Still, Dorian is
forecast to become a dangerous major hurricane later and maintain
that status as it heads for the northwestern Bahamas and the
Florida peninsula.
Key Messages:
1. A Hurricane Watch is now in effect for the northwestern Bahamas,
where the risk of life-threatening storm surge and hurricane-force
winds this weekend has continued to increase. Residents should
begin to execute their hurricane plans and listen to advice given
by local emergency officials.
2. There is an increasing likelihood of a prolonged period of
hazardous weather conditions that could last for a couple of days
in parts of Florida early next week.
3. The risk of life-threatening storm surge along portions of the
Florida east coast has increased, although it is too soon to
determine where the highest storm surge will occur. The risk of
devastating hurricane-force winds along the Florida east coast and
peninsula early next week has also increased, although it is too
soon to determine where the strongest winds will occur. Residents
should have their hurricane plan in place, know if they are in a
hurricane evacuation zone, and listen to advice given by local
emergency officials.
4. Regardless of the exact track of Dorian, heavy rains are expected
to occur over portions of the Bahamas, Florida, and elsewhere in the
southeastern United States this weekend and into the middle of next
week.
FORECAST POSITIONS AND MAX WINDS
INIT 30/0900Z 23.8N 69.1W 90 KT 105 MPH
12H 30/1800Z 24.8N 70.3W 100 KT 115 MPH
24H 31/0600Z 25.6N 72.0W 105 KT 120 MPH
36H 31/1800Z 26.1N 73.8W 110 KT 125 MPH
48H 01/0600Z 26.4N 75.5W 115 KT 130 MPH
72H 02/0600Z 26.7N 78.3W 120 KT 140 MPH
96H 03/0600Z 26.9N 80.1W 115 KT 130 MPH...INLAND
120H 04/0600Z 28.1N 81.4W 65 KT 75 MPH...INLAND
$$
Forecaster Berg
