Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sat Sep 23 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Maria, located a few hundred miles east of Nassau, Bahamas, and on
Tropical Storm Lee, located over the central Atlantic Ocean almost
a thousand miles east of Bermuda.

Tropical cyclone formation is not expected during the next 5 days.

&&

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

$$
Forecaster Berg

TINY LEE MOVING SLOWLY NORTHWARD

Tropical Storm Lee Discussion Number 20
NWS National Hurricane Center Miami FL AL142017
500 AM AST Sat Sep 23 2017

Not much has changed with Lee over the past six hours. The
convection previously observed in the SE quadrant appears to have
rotated around the tropical storm and faded, but a 0609 UTC SSMI
overpass indicates that a new burst has since taken its place.
Dvorak intensity estimates range from 30 to 35 kt, so the intensity
has been held at 35 kt for this advisory.

Every aspect of the forecast is highly uncertain. With regards to
intensity, the model forecasts range from dissipation (GFS) to
a category 2 or 3 hurricane (HWRF, HMON). Since the environment
still appears to be generally favorable for intensification, my
forecast remains close to the HWRF, and a little above the intensity
consensus through 72 h. The forecast shows gradual weakening after
that time as the shear increases. Because Lee is so small, it is
very possible that the tropical storm could strengthen far more
quickly than indicated here, at just about any time during the
forecast period. Likewise, rapid weakening could occur later in the
period if the shear increases like the SHIPS diagnostics indicate it
will.

As uncertain as the intensity forecast is, the track forecast may be
even more so. The ECMWF now shows a relatively deep Lee drifting
south for the next 72 hours, followed by a gradual turn toward the
northwest. On the other hand, the GFS continues to depict a shallow
Lee (or its remnants) moving steadily eastward through the forecast
period. As a result, these two typically reliable models differ by
more than 900 miles at day 5. The new official track forecast is
generally close to the corrected consensus models, FSSE and HCCA,
but hedges somewhat toward the ECMWF since it’s version of Lee is
more in line with the NHC intensity forecast. As a result, the NHC
track forecast has been shifted significantly to the west,
especially at 72 h and beyond, but still lies nearly 400 miles to
the east of the ECMWF.

Needless to say, confidence in the forecast is low, and significant
changes to the track or intensity forecast may be required during
the next day or two.

FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 31.9N 49.2W 35 KT 40 MPH
12H 23/1800Z 32.3N 49.1W 40 KT 45 MPH
24H 24/0600Z 32.5N 48.4W 45 KT 50 MPH
36H 24/1800Z 32.2N 47.4W 50 KT 60 MPH
48H 25/0600Z 31.7N 46.2W 60 KT 70 MPH
72H 26/0600Z 30.5N 44.5W 75 KT 85 MPH
96H 27/0600Z 29.8N 45.0W 70 KT 80 MPH
120H 28/0600Z 30.5N 46.5W 60 KT 70 MPH

$$
Forecaster Zelinsky

WARNINGS DISCONTINUED FOR THE BAHAMAS AND THE TURKS AND CAICOS ISLANDS… …HIGH SWELLS ARE EXPECTED TO INCREASE ALONG PORTIONS OF THE SOUTHEAST UNITED STATES COAST

Hurricane Maria Discussion Number 29
NWS National Hurricane Center Miami FL AL152017
500 AM EDT Sat Sep 23 2017

Maria is sending mixed signals regarding its intensity this
morning. One one side, the 35 n mi wide eye has become better
defined in satellite imagery, and the last report from an Air Force
Reserve Hurricane Hunter aircraft indicated that the central
pressure had fallen to 952 mb. On the other side, the
aircraft-reported winds decreased a little since the previous
advisory, with maximum 700-mb flight-level winds of 110 kt and
maximum surface wind estimates from the Stepped Frequency Microwave
Radiometer near 100 kt. Based on the aircraft winds, the initial
intensity is lowered to 105 kt. Various analyses show that Maria is
experiencing about 15 kt of southwesterly shear, which is likely the
reason for an asymmetric distribution of convection in the eyewall
at this time.

The hurricane is likely to stay over warm water in an environment
of light to moderate shear for the next 36-48 h. The intensity
forecast during this time will show some fluctuations in strength,
with the forecast lying near the upper edge of the intensity
guidance. After 48 h, the forecast track takes Maria over the cold
sea surface temperatures left behind by former hurricane Jose,
which are below 26C in some areas. This should cause a pronounced
weakening, and the new forecast is similar to the old forecast
in showing such a trend during this time.

The initial motion remains 345/8. Maria is currently being steered
by a subtropical ridge to the east of the hurricane and a mid- to
upper-level trough over the southeastern United States. This
combination should cause a north-northwestward to northward motion
for the next couple of days. After that, the ridge is forecast to
amplify toward the northwest due to the influence of a mid- to
upper-level ridge in the westerlies moving through the northeastern
United States. The track guidance has responded to this evolution
by shifting westward since the last advisory, with several of the
global models now calling for Maria to come close enough to the
U. S. east coast to cause direct impacts before the system recurves
into the westerlies around 120 h. The latter part of the forecast
track is also shifted to the west, but it lies to the east of the
consensus models and the center of the guidance envelope. If the
current model trends continue, additional westward adjustments to
the track forecast will be necessary later today.

KEY MESSAGES:

1. Swells from Maria are expected to increase along the coast of
the southeastern United States and will likely cause dangerous surf
and life-threatening rip currents for the next several days.

3. Maria will likely move between the east coast of the United
States and Bermuda by the middle of next week. While the forecast
track has moved closer to the U. S. east coast, it is still too soon
to determine what, if any, direct impacts there might be in these
areas.

4. For more information on the flooding and rip current hazards in
the United States, please monitor information from your local
National Weather Service forecast office at www.weather.gov.

FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 24.8N 72.0W 105 KT 120 MPH
12H 23/1800Z 26.0N 72.4W 110 KT 125 MPH
24H 24/0600Z 27.7N 72.7W 110 KT 125 MPH
36H 24/1800Z 29.2N 72.9W 105 KT 120 MPH
48H 25/0600Z 30.3N 73.0W 100 KT 115 MPH
72H 26/0600Z 32.0N 73.0W 85 KT 100 MPH
96H 27/0600Z 34.0N 73.0W 70 KT 80 MPH
120H 28/0600Z 36.0N 71.5W 65 KT 75 MPH

$$
Forecaster Beven