Official Discussion issued by the National Hurricane Center

Isaias (AL092020) DATA RELEASED: 8/3/2020 9:00:00 AM UTC

Copy of official data

Tropical Storm Isaias Discussion Number  25
NWS National Hurricane Center Miami FL       AL092020
500 AM EDT Mon Aug 03 2020

Isaias continues to produce an area of vigorous convection near and
to the northeast of its low-level center.  Overnight radar data from
Melbourne and Jacksonville have shown a transient mid-level eye
feature that is located northeast of the low-level center.  The
earlier Air Force Reserve Hurricane Hunter aircraft flew near that
feature before departing the storm and found 700-mb flight-level
winds of 71 kt, with the highest SFMR winds still around 60 kt,
which is the basis for the initial wind speed for this advisory.  
An Air Force Reserve and NOAA Hurricane Hunter aircraft will be 
investigating Isaias within the next several hours.

The vertical wind shear that has been plaguing Isaias is forecast
to abate slightly today as the storm turns north-northeastward. All
of the intensity models shows some slight strengthening during the
next 12 hours, and the global models also indicate some deepening.
As a result, the updated NHC intensity forecast calls for Isaias to
regain hurricane status before the system moves over the coast of 
the Carolinas.  The new intensity forecast has necessitated
the issuance of a hurricane warning for a portion of the coasts of
northern South Carolina and southern North Carolina. After
landfall, Isaias is forecast to gradually weaken, but given the fast
forward motion of the storm, strong winds are expected to spread
northward along the coast of the Mid-Atlantic and Northeast United
States.  The cyclone is forecast to be absorbed by a larger
extratropical low over Canada in 3-4 days.

Isaias is moving northward or 355/8 kt. The track forecast
reasoning remains the same as before.  The tropical storm is
expected to accelerate north-northeastward to northeastward ahead
of a large mid-level trough over the eastern United States during 
the next couple of days. The dynamical models are in good agreement
except for some slight differences in the forward speed of Isaias.
The NHC track forecast is near the multi-model consensus aids,
which have once again trended slightly faster.


Key Messages:

1. There is the danger of life-threatening storm surge inundation 
along portions of the immediate coastline and adjacent waterways of 
northeastern South Carolina and southern North Carolina. 
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. Isaias is forecast to regain hurricane strength before it
reaches the coast of northeastern South Carolina and southern
North Carolina, and hurricane conditions are expected in the
Hurricane Warning by this evening. Preparations should be rushed to
completion.

3. Tropical storm conditions are expected to spread northward 
within the Tropical Storm Warning area from Florida to portions of 
southern New England through Tuesday afternoon.  Tropical storm 
conditions are possible across other portions of New England within 
the Tropical Storm Watch area by early Wednesday.  Additional 
watches or warnings may be required later today.

4. Heavy rainfall will result in flash and urban flooding, some of 
which may be significant in the eastern Carolinas and the 
mid-Atlantic, 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.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 29.7N  79.9W   60 KT  70 MPH
12H  03/1800Z 31.3N  79.6W   65 KT  75 MPH
24H  04/0600Z 34.8N  78.1W   60 KT  70 MPH...INLAND
36H  04/1800Z 39.4N  75.2W   55 KT  65 MPH...INLAND
48H  05/0600Z 44.4N  71.5W   35 KT  40 MPH...INLAND
60H  05/1800Z 48.6N  68.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
72H  06/0600Z 52.0N  65.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
96H  07/0600Z...DISSIPATED

$$
Forecaster Brown/Berg