Skip Navigation Links
NOAA NOAA United States Department of Commerce

Post-Tropical Cyclone Isaias Forecast Discussion


Home   Public Adv   Fcst Adv   Discussion   Wind Probs   Graphics   Archive  

U.S. Watch/Warning   Local Products  


747 
WTNT44 KNHC 050246
TCDAT4

Post-Tropical Cyclone Isaias Discussion Number  32
NWS National Hurricane Center Miami FL       AL092020
1100 PM EDT Tue Aug 04 2020

Satellite and radar data, along with surface observations, indicate
that Isaias has lost its tropical cyclone characteristics as it
merges with a weak baroclinic zone over New England and
southeastern Canada.  Thus, it is being designated a post-tropical
cyclone.  The initial intensity is reduced to 40 kt based mainly on 
a recent observation at the Isle of Shoals, New Hampshire, and 
these winds are occurring over the Gulf of Maine well to the 
southeast of the center.  The post-tropical cyclone is expected to 
weaken further, with winds dropping below 35 kt early tomorrow.  
After that, the system is forecast to be absorbed into a large 
baroclinic low over southeastern Canada between 36-48 h.

The initial motion remains north-northeastward or 020/33 kt.  A
continued general north-northeastward motion with a decrease in
forward speed is expected until the cyclone is absorbed by the
larger low.  The new NHC track forecast is similar to the previous
forecast and is in the center of the tightly-clustered track
guidance models.

While Isaias is now post-tropical, the National Hurricane Center
will continue to issue advisories until the Tropical Storm Warning
can be discontinued along the coast of the United States.


Key Messages:

1. Tropical storm force winds that could cause tree damage and power
outages will continue over portions of New England for a few more
hours.

2. As the rainfall exits the United States, scattered minor to 
moderate and isolated major river flooding is ongoing or forecast 
across portions of the Mid-Atlantic with most rivers falling below 
flood stage Wednesday.  Quick-responding rivers in the Northeast 
will also be susceptible to minor and possible moderate river 
flooding.

3.  The threat of tornadoes will continue over portions of Maine 
for a few more hours.


FORECAST POSITIONS AND MAX WINDS

INIT  05/0300Z 45.3N  72.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 12H  05/1200Z 49.1N  71.1W   30 KT  35 MPH...POST-TROP/EXTRATROP
 24H  06/0000Z 52.6N  70.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
 36H  06/1200Z 54.0N  68.2W   25 KT  30 MPH...POST-TROP/EXTRATROP
 48H  07/0000Z...DISSIPATED

$$
Forecaster Beven