Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Thu Sep 28 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Maria, located a few hundred miles east-northeast of Cape
Hatteras, North Carolina, and on Hurricane Lee, located over the
central Atlantic Ocean several hundred miles east of Bermuda.

1. A large area of cloudiness and showers extending from the
northwestern Caribbean Sea across Cuba to the Bahamas is associated
with a broad surface trough interacting with an upper-level low. A
weak area of low pressure is likely to form from this weather system
while it moves northward across Cuba and near the east coast of
the Florida peninsula during the next few days, and environmental
conditions appear conducive for development before upper-level winds
become less favorable early next week. Regardless of development,
this system is likely to produce locally heavy rainfall over
portions of Cuba, southern Florida, the Florida Keys, and the
Bahamas during the next several days.
* Formation chance through 48 hours…low…20 percent.
* Formation chance through 5 days…medium…40 percent.

Forecaster Stewart

LEE EXPECTED TO ACCELERATE NORTHEASTWARD OVER THE CENTRAL ATLANTIC

Hurricane Lee Discussion Number 41
NWS National Hurricane Center Miami FL AL142017
500 AM AST Thu Sep 28 2017

Although Lee remains a powerful hurricane, the cloud pattern
appears to be gradually losing some organization. The eye has
become ragged at times, and the convective pattern is now more
asymmetric with convection becoming limited over the northwestern
quadrant. The initial wind speed is held at 95 kt, based on an
average of the Dvorak CI-numbers from TAFB/SAB and CIMSS at the
University of Wisconsin, but this could be a little generous.

Lee is headed toward an environment of strong wind shear and cooler
waters. These more hostile conditions should cause the system to
steadily weaken during the next couple of days, and Lee will likely
fall below hurricane strength in 36 to 48 hours. The system is
expected to lose its tropical characteristics in a little more than
2 days when it will be over SSTs below 20 deg C and in an
environment of about 30 kt of westerly shear. Dissipation is now
predicted to occur by day 3, in agreement with the latest runs of
the GFS and ECMWF models. The NHC intensity forecast is an update
of the previous one, and it remains in good agreement with the ICON
and HCCA consensus aids.

Lee has turned to the north at 8 kt on the western side of a
mid-level ridge. The hurricane is forecast to begin accelerating
to the northeast later today when it becomes embedded in fast
mid-latitude flow, and it should continue moving in that direction
until it dissipates. The models are tightly clustered, and only
minor changes were made to the previous NHC track forecast.

FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 32.5N 57.2W 95 KT 110 MPH
12H 28/1800Z 34.5N 56.3W 90 KT 105 MPH
24H 29/0600Z 37.4N 53.4W 75 KT 85 MPH
36H 29/1800Z 41.0N 47.7W 65 KT 75 MPH
48H 30/0600Z 44.7N 39.4W 55 KT 65 MPH
72H 01/0600Z…DISSIPATED

$$
Forecaster Cangialosi

MARIA WEAKENS TO A TROPICAL STORM

Tropical Storm Maria Discussion Number 49
NWS National Hurricane Center Miami FL AL152017
500 AM EDT Thu Sep 28 2017

Maria’s satellite presentation has not changed much during the past
six hours, with 15-20 kt of northwesterly shear continuing to
displace much of the deep convection to the east of the center.
Despite the discrepancy between aircraft observations and Dvorak
estimates noted yesterday, a pair of ASCAT passes from a few hours
ago showed maximum winds in the 50-55 kt range. Even with the
assumption that the resolution of the ASCAT data may not have
revealed the highest winds, an analysis suggests that Maria has
weakened back to a 60-kt tropical storm. Little change in intensity
is anticipated during the next two days while Maria moves over sea
surface temperatures of 26-27 degrees Celsius, and while vertical
shear decreases during the next 24 hours. After 48 hours, a marked
jump in shear and much colder waters should induce more weakening,
and model guidance indicates that Maria should complete
extratropical transition by day 3. The extratropical low should
then be absorbed by a larger system over the northeastern Atlantic
by day 4. This scenario is in agreement with guidance provided by
the NOAA Ocean Prediction Center.

Maria is becoming embedded in the mid-latitude westerlies and is
now moving toward the east-northeast, or 060/7 kt. The cyclone is
expected to turn eastward very soon, but then turn back toward the
east-northeast in 36 hours as a positively tilted trough moves off
the New England and Atlantic Canada coasts. The speed differences
among the track models are not as significant as they were
yesterday, although the updated NHC track forecast was nudged
southward for much of the forecast period to follow an overall
modest shift in the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 36.8N 71.0W 60 KT 70 MPH
12H 28/1800Z 36.8N 68.8W 55 KT 65 MPH
24H 29/0600Z 37.0N 64.9W 55 KT 65 MPH
36H 29/1800Z 38.0N 59.7W 55 KT 65 MPH
48H 30/0600Z 40.0N 53.1W 55 KT 65 MPH
72H 01/0600Z 46.4N 35.5W 45 KT 50 MPH…POST-TROP/EXTRATROP
96H 02/0600Z…DISSIPATED

$$
Forecaster Berg