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Hurricane Isaias Forecast Discussion


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000
WTNT44 KNHC 040300
TCDAT4

Hurricane Isaias Discussion Number  28
NWS National Hurricane Center Miami FL       AL092020
1100 PM EDT Mon Aug 03 2020

NWS Doppler radar data and reports from an Air Force Reserve 
Hurricane Hunter aircraft indicate that Isaias re-intensified to a 
hurricane despite a less than impressive appearance in satellite 
imagery.  The aircraft reported 117 kt winds at 700 mb to the 
east of the center, but these were not mixed to the surface by 
the weak convection in that area, as the maximum SFMR winds were 75 
kt.  Based on these data, the initial intensity is raised to 75 kt.

The hurricane is moving 020/19, and a faster forward speed is 
expected as the system moves farther into the mid-latitude 
southwesterly flow.  This should bring the center onshore in 
southern North Carolina shortly, followed by a track through the 
mid-Atlantic and western New England states Tuesday and Tuesday 
night and into southeastern Canada early Wednesday.

Interaction with a strong jet stream suggests that Isaias should 
weaken more slowly than normal as it moves through the eastern 
United States, and this should produce very strong wind gusts along 
the mid-Atlantic coast tomorrow. As a result, the gust factors at 
24-48 h have been increased above the standard 20 percent in the
Forecast/Advisory (TCMAT4). The cyclone is forecast to be absorbed
by a larger extratropical low over Canada in about 72 h.

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 the North Carolina coast, including
portions of Pamlico and Albemarle Sounds. Residents in these
areas should follow advice given by local emergency officials.

2. Hurricane conditions are spreading into the southern portion of 
the hurricane Warning area and should spread northward through 
tonight and early tomorrow morning.

3. Isaias is expected to bring widespread sustained tropical storm
force winds and wind gusts to hurricane force to the mid-Atlantic
coast, including portions of the Chesapeake Bay region, later 
tonight and on Tuesday, which could cause tree damage and power 
outages. Tropical storm conditions are expected to spread across 
New England late Tuesday into early Wednesday.

4. Heavy rainfall along the East Coast near the path of Isaias will
result in flash and urban flooding, some of which may be significant
in the eastern Carolinas, mid-Atlantic and northeast through
Wednesday. Widespread minor to moderate river flooding is possible
across portions of the Carolinas and the Mid-Atlantic. Quick-
responding rivers in the northeast will also be susceptible to minor
river flooding.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 33.8N  78.5W   75 KT  85 MPH
 12H  04/1200Z 37.0N  76.8W   60 KT  70 MPH...INLAND
 24H  05/0000Z 42.0N  73.8W   50 KT  60 MPH...INLAND
 36H  05/1200Z 46.8N  70.4W   40 KT  45 MPH...INLAND
 48H  06/0000Z 50.8N  68.3W   30 KT  35 MPH...POST-TROP/EXTRATROP
 60H  06/1200Z 52.9N  66.3W   25 KT  30 MPH...POST-TROP/EXTRATROP
 72H  07/0000Z...DISSIPATED

$$
Forecaster Beven