Isaias Downgraded To A Tropical Storm

00

FXUS61 KCAR 020429

AFDCAR

Area Forecast Discussion

National Weather Service Caribou ME

1229 AM EDT Sun Aug 2 2020

.SYNOPSIS...

High pressure will crest over the area late tonight and move

southeast Sunday. Low pressure will lift west of the area Sunday

night and track to our north Monday. A cold front will cross

the area Monday night. Isaias, or its remnants, will track

across the region Wednesday. High pressure will build late week.....

.........SHORT TERM /TONIGHT THROUGH TUESDAY/...

Low pressure lifting well west of the region will bring a breezy and

increasingly humid night Sunday night as a southerly breeze pulls

moist air north. Some spotty light showers and drizzle are possible.

Otherwise, the night will be mostly cloudy. Low pressure will lift

north of the area Monday pulling a weak cold front in. Moisture and

a significant mechanisms for lift are weak so only spotty showers or

an isolated thunderstorms will be possible Monday with the front,

mainly across the north. The front will dissipate over the region

Monday night bringing a tranquil night. Moisture will begin sliding

north well ahead of tropical system Isaias with some light rain or

drizzle possibly reaching Downeast areas by early Tuesday morning.

Moisture will deepen Tuesday ahead of the approaching system

increasing the chances for rain over the area. Rain will become

likely in western parts of the region by late Tuesday with a chance

of rain or drizzle elsewhere. Some of the rain will be supported by

upper level difluence between the subtropical high to our southeast

and a trough of low pressure centered just north of the Great

Lakes.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Isaias should approach Tuesday night, cross the region Wednesday,

then exit across the Maritimes Wednesday night. However, the exact

timing of the storm is still uncertain. Uncertainty also exists

regarding the storms eventual track and intensity. Isaias is

currently forecast to be a tropical storm while impacting the

forecast area. Winds, along with rainfall, will be dependent on both

the eventual track and intensity of the storm. The strength and

organization will be largely dependent on the amount of time the

storm tracks over land or water during the approach to the forecast

area. A more inland approach would tend to support a weaker storm,

while a more over water approach would tend to support a stronger

system. An upper trof approaching from the west could act to enhance

rainfall with the system. Expect rain, along with a chance of

thunderstorms, to expand across the region Tuesday night then

persist with the system Wednesday. Rainfall will then diminish later

Wednesday into Wednesday night in the wake of the storm. The upper

trof will cross the region Thursday, which could support a slight

chance of showers across mostly the north and mountains. Otherwise,

partly cloudy skies are expected Thursday. High pressure is expected

early Friday, with an upper level/surface trof approaching late.

Generally expect partly cloudy/mostly clear skies across the region

Friday, though could again have the slight chance of a diurnal

shower across mostly the north and mountains. The upper

level/surface trof will support a chance of diurnal showers across

mostly the north and mountains Saturday. Otherwise, expect generally

partly cloudy skies Saturday. Near normal, to slightly above

normal, level temperatures are expected Wednesday through

Saturday........

954 

WTNT44 KNHC 020256

TCDAT4

Tropical Storm Isaias Discussion Number  20

NWS National Hurricane Center Miami FL       AL092020

1100 PM EDT Sat Aug 01 2020

Deep convection has increased this evening in a cluster to the east

and northeast of the aircraft-observed center position.  Radar data

suggests a mid-level center or vorticity maximum in that area,

which is between Grand Bahama and Andros Island.  Observations from

the Air Force Hurricane Hunters indicate that Isaias has not

restrengthened thus far, but there is still a small window of

opportunity for it to regain hurricane intensity Sunday while

passing over the Gulf Stream waters.  Synoptic surveillance data

from the NOAA Gulfstream-IV aircraft indicate that the upper-level

west-southwesterly flow over Isais will begin to increase by late

Sunday.  The resulting increase in shear and interaction with land

should cause weakening beyond 24 hours, and the official intensity

forecast is near or above the intensity model consensus.

Assuming that the aforementioned mid-level feature is not the 

dominant center of circulation, the aircraft fixes give a motion 

estimate of about 310/8 kt.  Isais has been moving northwestward 

along the southwestern periphery of a mid-level high pressure area. 

An approaching trough near the Ohio Valley is expected to cause the 

tropical cyclone to turn northward within 48 hours.  After that, 

Isaias should accelerate north-northeastward to northeastward ahead 

of the trough, and move near or over the east coast of the United 

States. The official track forecast remains close to both the 

simple and corrected dynamic model consensus tracks, TVCN and HCCA 

respectively.

Key Messages:

1. Hurricane conditions and dangerous storm surge will continue in

portions of the northwest Bahamas through Sunday morning.

2. Hurricane conditions are expected along portions of the Florida

east coast on Sunday with tropical storm conditions expected to

begin late tonight.  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 there should follow advice given

by local emergency officials.

4. Isaias will produce heavy rains and potentially life-threatening

flash flooding in the Bahamas, and flash and urban flooding,

especially in low-lying and poorly drained areas, along the east

coast of the United States. Minor river flooding and isolated

moderate river flooding is possible across portions of the Carolinas

and mid Atlantic early next week.

5. Tropical storm watches and warnings are in effect for portions of

the United States East Coast from northeast Florida to South

Carolina. Additional watches and warnings will likely be issued

on Sunday as Isaias is expected to move northward near or over the

southeast and mid-Atlantic coasts early next week.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 25.5N  79.1W   60 KT  70 MPH

 12H  02/1200Z 26.6N  79.9W   65 KT  75 MPH

 24H  03/0000Z 28.0N  80.5W   65 KT  75 MPH...ON COAST

 36H  03/1200Z 29.7N  80.8W   60 KT  70 MPH

 48H  04/0000Z 32.0N  80.0W   55 KT  65 MPH

 60H  04/1200Z 35.3N  78.1W   50 KT  60 MPH...INLAND

 72H  05/0000Z 39.7N  74.8W   40 KT  45 MPH...INLAND

 96H  06/0000Z 47.0N  66.0W   35 KT  40 MPH...POST-TROP/INLAND

120H  07/0000Z 51.5N  57.5W   30 KT  35 MPH...POST-TROP/INLAND

$$

Forecaster Pasch