[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 010245
TCDAT4

Hurricane Isaias Discussion Number  16
NWS National Hurricane Center Miami FL       AL092020
1100 PM EDT Fri Jul 31 2020

Isaias has a somewhat asymmetrical appearance on satellite images,
with lots of deep convection over the eastern semicircle and not as
much over the western part of the circulation.  Reports from an Air
Force Hurricane Hunter aircraft indicate that the central pressure
has dropped a few mb, and flight-level and SFMR-observed surface
wind observations from the aircraft indicate an intensity of near
70 kt.  The hurricane is experiencing some westerly shear, and this
is likely to limit intensification.  However, some strengthening is
still possible on Saturday.  When Isais moves farther north in a
couple of days, the shear should cause a gradual weakening trend to
begin.  The official intensity forecast is about the same as the
previous one, and a little above the model consensus.

The hurricane continues moving northwestward at a bit slower pace,
or 310/13 kt.  The general track forecast philosophy has not
changed.  Isais should continue to move northwestward on the
southwest side of a mid-level ridge through Saturday and begin to
turn north-northwestward through a weakness in the ridge on Sunday.
Thereafter, a turn toward the north-northeast and northeast with an
increase in forward speed is likely during days 3 to 5.  The
official track forecast is close to the previous one and also very
close to the latest dynamical model consensus.

The hurricane warning has been extended northward along the Florida
east coast.


Key Messages:

1. Hurricane conditions and dangerous storm surge are expected in
portions of the Bahamas through Saturday, and Hurricane Warnings
are in effect.

2. Hurricane conditions are expected along portions of the Florida
east coast late Saturday and Saturday night, and a Hurricane Warning
has been issued.  Preparations to protect life and property should
be rushed to completion.

3. Dangerous storm surge is possible along the Florida east coast
from Jupiter Inlet to Ponte Vedra Beach where water rises of 2 to 4
feet above ground level are possible along the immediate coastline
and adjacent waterways. Residents in these areas should follow
advice given by local emergency officials.

4. Isaias will produce heavy rains and potentially life-threatening
flash and urban flooding, especially in low-lying and poorly drained
areas, across South to east-Central Florida, and across the
Carolinas to the mid Atlantic. Isolated minor river flooding is
possible across the eastern Carolinas and into Virginia early next
week.

5. There is a risk of impacts from winds, heavy rainfall, and storm
surge spreading along much of the the U.S. east coast through early
next week, and interests there should monitor the progress of Isaias
and updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 23.3N  76.4W   70 KT  80 MPH
 12H  01/1200Z 24.5N  77.8W   75 KT  85 MPH
 24H  02/0000Z 25.9N  79.1W   75 KT  85 MPH
 36H  02/1200Z 27.1N  80.0W   70 KT  80 MPH
 48H  03/0000Z 28.5N  80.5W   65 KT  75 MPH
 60H  03/1200Z 30.2N  80.5W   60 KT  70 MPH
 72H  04/0000Z 33.1N  78.9W   60 KT  70 MPH
 96H  05/0000Z 41.0N  72.5W   55 KT  65 MPH
120H  06/0000Z 47.5N  64.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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