4 Sep Tue 2018

Tropical Storm Florence Discussion Number 20
NWS National Hurricane Center Miami FL AL062018
500 AM AST Tue Sep 04 2018

Florence’s cloud pattern has changed very little during the past
several hours, with the exception of a possible small Central Dense
Overcast developing just to the east of the center. An earlier
AMSR2 overpass revealed a rather obvious tilt toward the
east-northeast, indicative of the moderate southwesterly shear.
The initial intensity is held a 60 kt, and is supported by the
Dvorak subjective and objective T-numbers.

Florence should exhibit little change in strength during the next
24 hours or so, as the cyclone traverses marginally warm sea surface
temperatures and is influenced by modest west-southwesterly shear.
Slight weakening is expected during the mid- forecast period as the
shear gradually increases with time. Afterward, the upper-level
wind environment should become a little more favorable and, at the
same time, Florence will be moving back over warmer SSTs.
Consequently, the cyclone should gradually strengthen through day 5.
This forecast is unchanged from the previous one, and is in good
agreement with the NOAA-HCCA guidance.

The initial motion estimate is west-northwestward, or 290/11 kt.
The cyclone is expected to be steered west-northwestward for the
next 48 hours by a mid- to upper tropospheric ridge anchored to
the north, followed by a northwestward turn around the 72 hr period
as it enters a growing weakness in the aforementioned ridge. A
rather large spread in the global and hurricane models remains
particularly beyond day 4, however, the consensus models and the
global ensemble means have have been fairly consistent from run to
run. This forecast is just a bit to the north of the previous
advisory and just south of the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 04/0900Z 19.3N 42.0W 60 KT 70 MPH
12H 04/1800Z 19.9N 43.7W 60 KT 70 MPH
24H 05/0600Z 20.8N 45.8W 60 KT 70 MPH
36H 05/1800Z 21.8N 48.0W 55 KT 65 MPH
48H 06/0600Z 22.9N 50.2W 50 KT 60 MPH
72H 07/0600Z 25.2N 53.4W 50 KT 60 MPH
96H 08/0600Z 27.1N 55.6W 55 KT 65 MPH
120H 09/0600Z 29.1N 57.7W 65 KT 75 MPH

$$
Forecaster Roberts

Tropical Storm Gordon Discussion Number 8
NWS National Hurricane Center Miami FL AL072018
400 AM CDT Tue Sep 04 2018

Gordon has changed little in organization on geostationary
satellite images or on the WSR-88D radar presentation over the past
several hours. The storm has a small CDO with convective banding
features primarily over the eastern semicircle of the circulation.
Overall the cloud pattern is indicative of moderate westerly shear
over the system, likely associated with an upper-level trough near
the central Gulf of Mexico. An Air Force Reserve Unit Hurricane
Hunter aircraft investigated Gordon a few hours ago and reported
maximum SFMR-measured surface winds of 54 kt. On this basis the
intensity had been adjusted to 55 kt, which is somewhat above the
latest Dvorak estimates. It is assumed that the shear will not be
strong enough to inhibit at least some strengthening before
landfall, so the tropical cyclone is still forecast to become a
hurricane later today. The official forecast, prior to landfall, is
close to the latest LGEM intensity guidance, and near the upper end
of the guidance suite. Gordon should weaken rapidly after landfall
in the lower Mississippi Valley region.

The motion continues west-northwestward, or 300/15 kt. There is
little or no change to the NHC track prediction or forecast
reasoning from the previous advisory. Gordon is expected to move
along the southwestern periphery of a mid-level high pressure area
and make landfall along the north-central Gulf of Mexico coast
within 24 hours. After landfall, the cyclone is forecast to move
northwestward, along the western side of the high, at a reduced
forward speed. Late in the forecast period Gordon, or its
post-tropical remnant, should turn northward to north-northeastward
as it approaches the mid-latitude westerlies. The official track
forecast is near the model consensus and very close to the previous
NHC track.

Key Messages:

1. Gordon is expected to bring life-threatening storm surge and
hurricane conditions to portions of the central Gulf Coast where a
Storm Surge Warning and Hurricane Warning are in effect. Residents
in these areas should listen to advice from their local officials.
All preparations to protect life and property should be rushed to
completion, as tropical storm conditions are expected to arrive in
the warning areas this afternoon.

2. Heavy rainfall from Gordon will affect the western Florida
Panhandle, southern Alabama, southern Mississippi and Louisiana,
where totals could reach as high as 12 inches. This rainfall could
cause flash flooding.

FORECAST POSITIONS AND MAX WINDS

INIT 04/0900Z 27.7N 85.7W 55 KT 65 MPH
12H 04/1800Z 29.0N 87.5W 65 KT 75 MPH
24H 05/0600Z 30.7N 89.6W 55 KT 65 MPH…INLAND
36H 05/1800Z 32.2N 91.0W 35 KT 40 MPH…INLAND
48H 06/0600Z 33.4N 92.3W 25 KT 30 MPH…INLAND
72H 07/0600Z 34.9N 94.3W 20 KT 25 MPH…POST-TROP/REMNT LOW
96H 08/0600Z 37.0N 94.5W 20 KT 25 MPH…POST-TROP/REMNT LOW
120H 09/0600Z 40.0N 92.0W 20 KT 25 MPH…POST-TROP/REMNT LOW

$$
Forecaster Pasch