Aug 19 Saturday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sat Aug 19 2017

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Harvey, located over the eastern Caribbean Sea.

1. A trough of low pressure located about 300 miles east-northeast of
the northern Leeward Islands continues to produce disorganized
showers and thunderstorms. Environmental conditions are expected to
be only marginally conducive for development during the next few
days while this system moves west-northwestward at about 20 mph.
* Formation chance through 48 hours…low…20 percent.
* Formation chance through 5 days…medium…40 percent.

2. A tropical wave located over the eastern Atlantic Ocean about
midway between the Lesser Antilles and Africa is producing some
shower and thunderstorm activity. Environmental conditions appear
somewhat conducive for gradual development over the next few days
while the system moves west-northwestward to northwestward at about
20 mph, but upper-level winds are forecast to become unfavorable by
early next week.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…low…20 percent.

Forecaster Beven

HEAVY RAINFALL THREAT TODAY IN THE ABC ISLANDS FROM HARVEY

Tropical Storm Harvey Discussion Number 8
NWS National Hurricane Center Miami FL AL092017
500 AM AST Sat Aug 19 2017

GOES-16 shortwave infrared imagery shows the partially exposed
center of Harvey on the eastern edge of a large area of deep
convection. While the center is closer to the convection than a few
hours ago, cirrus clouds be clearly seen moving from northeast to
southwest across the system; an indication of the persistent shear.
Satellite estimates suggest the maximum winds of Harvey remain 35
kt.

The storm has picked up some forward speed with a recent motion
estimate of 275/18. A low- to mid-level ridge extending across the
western Atlantic should keep Harvey on a fast westward course across
the Caribbean Sea for the next 48 hours. Thereafter, the ridge
weakens across the Gulf of Mexico due to a strong mid/upper-level
low currently seen there on water vapor images. This steering flow
change should cause Harvey to slow down and turn a little more to
the west-northwest in the northwestern Caribbean Sea, with an even
slower motion forecast for Harvey in the Bay of Campeche. Model
guidance is in fairly good agreement on this scenario, and no
significant changes were made to the previous forecast.

Harvey should be moving into a more conducive environment for
strengthening early next week since the strong northeasterly shear
that has been affecting the cyclone is forecast by almost all of the
guidance to weaken within about 24 hours. In a few days, most of
the global models show a favorable upper-level environment for
intensification, and Harvey could be near hurricane strength between
the 72 hour forecast period and landfall. There has been little
change to the guidance so the new intensity forecast is similar to
the previous one, close to the model consensus. However, with
a weak storm moving so quickly across the central Caribbean, one
always has to be careful of the system opening up into a wave. This
is a plausible alternative scenario still suggested by the GFS and
ECMWF models.

FORECAST POSITIONS AND MAX WINDS

INIT 19/0900Z 13.8N 65.9W 35 KT 40 MPH
12H 19/1800Z 14.0N 68.7W 35 KT 40 MPH
24H 20/0600Z 14.3N 72.7W 40 KT 45 MPH
36H 20/1800Z 14.6N 76.7W 45 KT 50 MPH
48H 21/0600Z 15.2N 80.1W 50 KT 60 MPH
72H 22/0600Z 17.0N 86.5W 55 KT 65 MPH
96H 23/0600Z 18.3N 90.5W 35 KT 40 MPH…INLAND
120H 24/0600Z 19.3N 93.0W 40 KT 45 MPH…OVER WATER

$$
Forecaster Blake