Aug 18 Friday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Fri Aug 18 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Harvey, located near Barbados.

1. Shower and thunderstorm activity associated with an area of low
pressure located about 750 miles east-northeast of the Leeward
Islands continues to show signs of organization. While it would
take only a slight increase in organization for a tropical
depression to form later today or tonight, upper-level winds are
becoming less favorable for development. The low is expected to
move west-northwestward at about 20 mph during the next few days,
and interests in the northern Leeward Islands should monitor the
progress of this disturbance.
* Formation chance through 48 hours…high…70 percent.
* Formation chance through 5 days…high…70 percent.

2. Shower activity has increased during the last 24 hours in
association with a tropical wave located over the far eastern
Atlantic Ocean, several hundred miles west-southwest of the Cabo
Verde Islands. Environmental conditions are forecast to become more
favorable for some development early next week while the system
moves west-northwestward to northwestward at about 20 mph.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…medium…40 percent.

Public Advisories on Harvey are issued under WMO header
WTNT34 KNHC and under AWIPS header MIATCPAT4.
Forecast/Advisories on Harvey are issued under WMO header
WTNT24 KNHC and under AWIPS header MIATCMAT4.

Forecaster Beven

CENTER OF HARVEY BETWEEN BARBADOS AND THE WINDWARD ISLANDS

Tropical Storm Harvey Discussion Number 4
NWS National Hurricane Center Miami FL AL092017
500 AM AST Fri Aug 18 2017

Harvey’s cloud pattern has changed very little in organization
during the past several hours. The low-level center is difficult to
find even using the 1-min images from GOES 16, but it appears to
be located on the eastern edge of the convection due to the
prevailing easterly shear. Dvorak estimates from both TAFB
and SAB support keeping the intensity at 35 kt. Another Air
Force plane will be investigating Harvey at sunrise.

The moderate easterly shear affecting the cyclone is expected to
increase a little during the next day or so, and this factor should
not allow significant strengthening. Once the cyclone reaches the
western Caribbean Sea in 3 or 4 days, an environment of lower shear
and high moisture is forecast to prevail, and Harvey should then
gather some strength. The cyclone could be near hurricane strength
by the time it is approaching Central America or the Yucatan
peninsula. The NHC forecast is very similar to the previous one and
is very close to the intensity consensus. The GFS and the ECMWF
global models are just a little more enthusiastic in keeping the
cyclone from dissipating in this last run, but who knows what they
might forecast the next time.

Harvey has not changed in track or speed, and it is still moving
toward the west or 270 degrees at 16 kt. The cyclone is well
embedded within the easterlies south of a persistent subtropical
ridge. This steering pattern will keep Harvey trapped in the
Caribbean Sea while moving westward for the next few days. The
track forecast is similar to the one issued by my predecessor and it
follows closely the multi-model consensus. The guidance envelope is
quite tight and is bounded by the northernmost ECMWF and the GFS to
the south.

FORECAST POSITIONS AND MAX WINDS

INIT 18/0900Z 13.1N 59.1W 35 KT 40 MPH
12H 18/1800Z 13.2N 61.7W 35 KT 40 MPH
24H 19/0600Z 13.5N 65.2W 40 KT 45 MPH
36H 19/1800Z 13.9N 68.8W 40 KT 45 MPH
48H 20/0600Z 14.1N 72.7W 50 KT 60 MPH
72H 21/0600Z 15.0N 80.2W 60 KT 70 MPH
96H 22/0600Z 16.5N 86.5W 60 KT 70 MPH
120H 23/0600Z 17.5N 90.0W 35 KT 40 MPH…INLAND

$$
Forecaster Avila