Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Tue Sep 26 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Maria, located a couple of hundred miles southeast of Cape
Hatteras, North Carolina, and on Hurricane Lee, located over the
central Atlantic Ocean.

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

$$
Forecaster Brown

LEE STILL STRENGTHENING AND MOVING A LITTLE FASTER WESTWARD

Hurricane Lee Discussion Number 33
NWS National Hurricane Center Miami FL AL142017
500 AM AST Tue Sep 26 2017

Lee’s cloud pattern has continued to become better organized this
evening. The eye has cleared out and has warmed to nearly 10
degrees Celsius, and the eye wall cloud tops have cooled to
-63 degrees Celsius. The initial intensity is increased modestly to
85 kt and is based on a blend of the subjective and objective Dvorak
T-numbers. It is worth noting that the ADT adjusted raw T-number
yields an estimated intensity of 97 kt based on an eye scene-type.

The previously noted southeasterly shear undercutting the diffluent
flow aloft has certainly diminished and should remain low for the
next 48 hours or so. During this initial period, Lee could get a
little stronger as indicated in the HWRF hurricane model and the
Decay-SHIPS. Afterward, increasing vertical shear, primarily due to
the outflow generated by Maria, and decreasing sea surface
temperatures should induce a gradual weakening trend as the cyclone
moves into a high latitude baroclinic zone and ultimately becomes an
extratropical cyclone in 4 days. The intensity forecast is
basically an update of 6 hours ago, and follows an average of the
IVCN and Florida State Superensemble guidance.

The initial motion is estimated to be westward, or 260/9 kt. The
cyclone is expected to continue moving within the easterly mid-level
steering flow, produced by a relatively narrow mid-tropospheric
ridge situated to the north, during the next 24 hours. Afterward,
a combination of a broad mid- to upper-level shortwave trough moving
out of the eastern Canadian Provinces and a subtropical ridge
building east of Lee should steer the hurricane gradually
northwestward and northward. On day 3 and beyond, Lee is forecast
to accelerate northeastward as it becomes embedded in a deep-layer
high latitude southwesterly flow downstream from the aforementioned
shortwave trough. Global models and the Cyclone Phase Evolution
analysis/forecast product show Lee become a extratropical
cyclone no later than day 4. The NHC forecast track is a little
south of the previous one through 48 hours, but similar
thereafter, and is based on the TVCX and HCCA consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 30.0N 52.5W 85 KT 100 MPH
12H 26/1800Z 29.9N 53.9W 90 KT 105 MPH
24H 27/0600Z 30.2N 55.4W 90 KT 105 MPH
36H 27/1800Z 30.9N 56.4W 90 KT 105 MPH
48H 28/0600Z 32.2N 56.6W 85 KT 100 MPH
72H 29/0600Z 36.9N 53.0W 75 KT 85 MPH
96H 30/0600Z 44.5N 40.2W 60 KT 70 MPH…POST-TROP/EXTRATROP
120H 01/0600Z 50.9N 22.0W 50 KT 60 MPH…POST-TROP/EXTRATROP

$$
Forecaster Roberts

MARIA CONTINUES TO MOVE NORTHWARD

Hurricane Maria Discussion Number 41
NWS National Hurricane Center Miami FL AL152017
500 AM EDT Tue Sep 26 2017

Maria is feeling the effects of the cool sea surface temperatures
left in the wake of Hurricane Jose. Satellite imagery shows that
the convective pattern is gradually losing organization, with the
remaining convection in a cluster to the southeast of the center
and in bands well to the east of the center. In addition, the
aircraft-reported central pressure has risen to 970 mb. While there
have been no observations of hurricane-force winds from the Stepped
Frequency Microwave Radiometer on the NOAA Hurricane Hunter
currently in the cyclone, it is likely that they still exist in
areas east of the center where the airplane has not yet sampled.
The initial intensity is lowered to a somewhat uncertain 65 kt based
mainly on the rising central pressure since the last advisory.

The combination of the cool water and moderate shear should cause
Maria to gradually weaken during the forecast period, with the
system now expected to weaken to a tropical storm in less than 24 h.
Near the 120 h point, the cyclone is expected to merge with a
frontal system and become extratropical. The new intensity forecast
is an update of the previous advisory.

The initial motion remains 360/6, with Maria moving northward on the
western side of the subtropical ridge. A mid- to upper-level ridge
over the northeastern United States to the north of the cyclone is
likely to keep the motion slow for the next 36-48 h. After that,
the mid-latitude westerlies are forecast to move southward across
the northeastern United States and break down the subtropical
ridge. This should lead to Maria turning east-northeastward and
accelerating after 48 h. The track guidance is in good agreement
with this scenario, and the new forecast track is close to the
previous track until 120 h, where it is nudged a bit to the south.
The track is also close to the center of the guidance envelope.

KEY MESSAGES:

1. Maria is forecast to continue moving northward, paralleling the
U.S. east coast for the next 36-48 hours, and it is likely that some
direct impacts will occur along portions of the North Carolina coast
beginning later today, where a Tropical Storm Warning is in effect.

2. Storm surge flooding, especially along the sound side of the
North Carolina Outer Banks, is expected beginning later today, and a
Storm Surge Watch has been issued for portions of eastern North
Carolina.

3. Swells generated by Maria are affecting much of the east coast of
the United States from Florida through southern New England. These
swells are also affecting Bermuda, Puerto Rico, the northern coast
of Hispaniola, the Turks and Caicos Islands, and the Bahamas. These
swells are likely to cause life-threatening surf and rip current
conditions. Please consult products from your local weather office
for more information.

FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 32.9N 73.1W 65 KT 75 MPH
12H 26/1800Z 33.7N 73.2W 65 KT 75 MPH
24H 27/0600Z 34.6N 73.1W 60 KT 70 MPH
36H 27/1800Z 35.4N 72.7W 60 KT 70 MPH
48H 28/0600Z 35.8N 71.7W 55 KT 65 MPH
72H 29/0600Z 37.0N 66.0W 55 KT 65 MPH
96H 30/0600Z 41.0N 53.0W 55 KT 65 MPH
120H 01/0600Z 48.0N 35.5W 55 KT 65 MPH…POST-TROP/EXTRATROP

$$
Forecaster Beven