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Tropical Storm ISAIAS (Text)


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Tropical Storm Isaias Discussion Number  24
NWS National Hurricane Center Miami FL       AL092020
1100 PM EDT Sun Aug 02 2020

Isais has not become better organized on satellite and radar imagery 
at this time.  The cyclone continues to produce vigorous deep 
convection but this convection continues to be displaced to the 
northeast of the center, and convective banding features are 
ill-defined.  Air Force Hurricane Hunter observations show that the 
central pressure has not fallen since earlier today, and 
flight-level and SFMR-observed surface wind measurements from the 
aircraft indicate that the intensity remains near 60 kt.  Although 
Isais will be moving through an environment of fairly strong 
southwesterly shear during the next day or so, it will also be 
traversing the warm waters of the Gulf Stream with its high oceanic 
heat content.  The latter factor could result in the system becoming 
a hurricane near landfall.  The official forecast is close to the 
intensity consensus, which keeps Isaias just below hurricane 
strength.

It should be emphasized that there is little difference between a 
strong tropical storm or a category 1 hurricane, in terms of 
impacts.

After landfall, the interaction with land and strong shear should 
result in steady weakening.  Based on the global models, the 
cyclone is likely to become an extratropical cyclone after it moves 
into Canada and dissipate over the north Atlantic shortly 
thereafter. 

The motion continues to be slightly west of due north or 345/8 kt.
There has been no significant change to the track forecast
reasoning.  Over the next couple of days, Isaias is expected to
accelerate north-northeastward on the east side of a large 500 mb
trough over the eastern United States and then turn northeastward
in 3 to 4 days as it moves through the mid-latitude westerlies.
The official track forecast is very close to the previous one and
similar to the latest corrected dynamical model consensus.  This is
between the GFS, which shows a slightly faster motion and the ECMWF,
which is slightly slower.
 

Key Messages:
 
1. There is the danger of life-threatening storm surge inundation of
2 to 4 feet above ground level from Edisto Beach South Carolina to
Cape Fear North Carolina along the immediate coastline and adjacent
waterways.  Life-threatening storm surge is possible along the
North Carolina coast from Cape Fear to Duck.  Residents in these
areas should follow advice given by local emergency officials.
 
2. Tropical storm conditions will spread northward within the
Tropical Storm Warning area from Florida to Maryland through
early Tuesday. Isaias is expected to be near hurricane strength when
it reaches the coast of northern South Carolina and southern North
Carolina Monday night, and strong tropical storm force winds are
likely with hurricane conditions possible in the Hurricane Watch
area.
 
3. Heavy rainfall from Isaias will continue to result in potentially
life-threatening flash flooding in the Northwest Bahamas through
tonight. Flash and urban flooding, some of which may be significant
in the eastern Carolinas and the mid-Atlantic, is expected through
midweek along and near the path of Isaias across the East Coast of
the United States. Widespread minor to moderate river flooding is
possible across portions of the Carolinas and the mid-Atlantic.
 
4. Tropical storm conditions are forecast to spread northward 
across the remainder of the U.S east coast on Tuesday and early 
Wednesday. A tropical storm watch is in effect through Long Island 
Sound and additional watches and warnings will likely be issued on 
Monday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0300Z 28.5N  79.8W   60 KT  70 MPH
 12H  03/1200Z 29.7N  80.0W   60 KT  70 MPH
 24H  04/0000Z 32.2N  79.3W   60 KT  70 MPH
 36H  04/1200Z 35.9N  77.3W   55 KT  65 MPH...INLAND
 48H  05/0000Z 40.5N  74.0W   40 KT  45 MPH...INLAND
 60H  05/1200Z 45.5N  70.0W   35 KT  40 MPH...INLAND
 72H  06/0000Z 50.0N  65.5W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  07/0000Z 55.5N  56.5W   25 KT  30 MPH...POST-TROP/EXTRATROP
120H  08/0000Z...DISSIPATED
 
$$
Forecaster Pasch
 
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Page last modified: Friday, 30-Oct-2020 12:09:18 UTC