Tropical Storm Isaias Forms

000

FXUS61 KCAR 310153

AFDCAR

Area Forecast Discussion

National Weather Service Caribou ME

953 PM EDT Thu Jul 30 2020

.SYNOPSIS...

A trough of low pressure will slowly move across the north through

Friday. High pressure will build in from the west on Saturday, crest

over the area Saturday night then move east on Sunday. Low pressure

will approach Sunday night and lift north of the area Monday. A cold

front will cross the region early Tuesday...........

.........LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

An upper trough will lift up to our northwest Sunday night as a

surface occlusion pushes into our region. Some difluence aloft

between the approaching trough and a subtropical high supported in

part by tropical system Isaias may enhance lift and shower activity.

The showers and isolated thunderstorms will continue into Monday and

possibly Monday night as the front slowly presses across our area. A

cold front will press south of the area Tuesday followed by some

cooler air being pulled in from beneath an upper trough in Quebec.

Subsidence behind this trough as it slides east combined with

surface high pressure should then bring a couple dry days Wednesday

into Thursday with some cumulus clouds Wednesday as the upper trough

pivots across. Thursday should turn out mostly sunny with the high

building over. Meanwhile, some of the long range forecast models

are bringing tropical storm Isaias near Maine during the mid-

week period next week. Forecast tracks range from just south of

the Gulf of Maine on the GFS to across southern Maine on the

ECMWF. The most inland tracks seem to be favored by guidance

solutions that show a deepening trough digging well to the west

and pulling the storm north. Track and intensity forecasts will

likely take a few days to refine but interests along the coast

should closely monitor forecast updates through the weekend and

into early next week.......

723 

WTNT44 KNHC 310235

TCDAT4

Tropical Storm Isaias Discussion Number  11

NWS National Hurricane Center Miami FL       AL092020

1100 PM EDT Thu Jul 30 2020

Isaias is beginning to form a small Central Dense Overcast, but 

much of the deep convection is situated over the eastern portion of 

the circulation.  Water vapor imagery suggests that upper-level 

outflow is modest to the northwest of the cyclone.  The southern 

portion of the system is still interacting with Hispaniola at this 

time.  Dvorak intensity estimates are 45 kt from SAB and 55 kt from 

TAFB so the current maximum wind speed is 50 kt for this advisory.  

An Air Force Hurricane Hunter aircraft is headed for Isaias and 

should soon provide a more precise intensity estimate.

Although southwesterly shear may limit strengthening of the system 

during the next couple of days, the environment should still be 

conducive enough for Isaias to become a hurricane in 24 to 36 hours. 

The official intensity forecast is similar to the previous one and 

a little above the model consensus.

The initial motion is a somewhat uncertain 305/16 kt.  There are no

basic changes to the track forecast or reasoning from the previous

advisory.  Isaias should continue to move generally northwestward on

the southern and southwestern side of a subtropical high pressure

area for the next day or so.  Then, as an approaching

mid-tropospheric trough erodes the high, a gradual turn toward the

north-northwest and north should occur.  In 3 to 5 days, the trough

should cause Isaias to turn toward the north-northeast and northeast

and accelerate.  The official track forecast is close to the

previous one and follows the latest simple and corrected dynamical

model consensus tracks.

Key Messages:

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

flash flooding and mudslides across the Dominican Republic, northern 

Haiti, Turks and Caicos, and the Bahamas.  

2. Hurricane or tropical storm conditions and dangerous storm surge 

are expected in portions of the northwestern and central Bahamas 

late Friday and Saturday, and Hurricane and Tropical Storm 

Warnings, respectively, are in effect for these areas. Preparations 

to protect life and property should be rushed to completion.  

Tropical storm conditions will continue to spread across portions 

of the Dominican Republic, Haiti, the Turks and Caicos and the 

southeastern Bahamas tonight through Friday, and Tropical Storm 

Warnings are in effect for these areas.

3. Tropical storm conditions are possible along portions of the

Florida east coast beginning Saturday, and a Tropical Storm Watch

is in effect.  While storm surge watches are not currently needed

for this area, they may be required on Friday if the forecast track 

shifts closer to the coast.  Heavy rains associated with Isaias may 

begin to affect South Florida and east-Central Florida beginning 

late Friday night, potentially resulting in isolated flash and urban 

flooding, especially in low-lying and poorly drained areas. 

4. There is a risk of impacts from winds, heavy rainfall, and storm

surge late this weekend from the northeastern Florida coast and 

spreading northward along the remainder of the U.S. east coast 

through early next week.  The details of the track and intensity 

forecast remain uncertain, and it is too soon to determine the 

magnitude and location of these potential impacts, but interests 

along the entire U.S. east coast should monitor the progress of 

Isaias and updates to the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 20.5N  71.9W   50 KT  60 MPH

 12H  31/1200Z 21.6N  73.9W   55 KT  65 MPH

 24H  01/0000Z 23.5N  76.1W   60 KT  70 MPH

 36H  01/1200Z 25.2N  77.8W   65 KT  75 MPH

 48H  02/0000Z 26.7N  79.0W   65 KT  75 MPH

 60H  02/1200Z 28.3N  79.6W   65 KT  75 MPH

 72H  03/0000Z 30.0N  79.5W   65 KT  75 MPH

 96H  04/0000Z 34.6N  76.8W   65 KT  75 MPH

120H  05/0000Z 42.0N  69.0W   60 KT  70 MPH

$$

Forecaster Pasch