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Tropical Storm Maria Discussion Number  51
NWS National Hurricane Center Miami FL       AL152017
500 PM AST Thu Sep 28 2017

After the earlier burst of convection near the center of Maria, the
overall convective pattern has become more ragged and cloud tops
have warmed. Westerly vertical shear has also displaced most of the
convective cloud shield to the east of the center. The most recent
Dvorak satellite intensity estimate from TAFB has decreased to 45
kt, and the latest UW-CIMSS ADT and SATCON values have decreased to
54 kt and 55 kt, respectively. Therefore, Maria's initial intensity
has been lowered to 55 kt for this advisory. Despite the ragged
satellite appearance, a 1431Z AMSU overpass indicated that Maria is
still a tropical cyclone based on a deep warm core that extends from
near the surface to above the 200 mb level, accompanied by a warm
anomaly of at least 2.5 deg C in the middle- and upper-levels of the
cyclone.

The initial motion estimate is 090/11 kt. Maria is forecast to move
in an easterly direction for the next 12 h or along the northern
edge of a strong deep-layer ridge located to its south. By 24 h,
acceleration and a turn toward the east-northeast is expected ahead
an approaching deep-layer trough. By 36-48 h, Maria is forecast to
turn toward the northeast and further accelerate, reaching forward
speeds of 30-35 kt when the cyclone will be moving over the far
North Atlantic. The latest track guidance continues to remain in
excellent agreement on this developing track scenario, and only a
slight nudge to the south of the previous forecast was required.

Little change in intensity is forecast during the next 36 h or so
while Maria remains over marginal SSTs of 25-26C and within a low to
moderate vertical wind shear environment. By 36 h and beyond, Maria
will be moving over sub-24C SSTs, reaching 21 deg C water by 48 h
or so. Increasing westerly wind shear of more than 40 kt should
induce a slow weakening trend, and Maria is now expected to become
extratropical by 48 h due to the aforementioned unfavorable
conditions. The extratropical low is forecast to be absorbed by a
larger low or frontal system over the northeastern Atlantic by 96 h,
before the low moves across Ireland. The intensity and wind radii
forecasts at 48 and 72 h are based on guidance provided by the NOAA
Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 36.8N  67.8W   55 KT  65 MPH
 12H  29/0600Z 37.1N  64.4W   55 KT  65 MPH
 24H  29/1800Z 38.1N  58.8W   55 KT  65 MPH
 36H  30/0600Z 40.0N  52.0W   55 KT  65 MPH
 48H  30/1800Z 42.7N  44.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  01/1800Z 48.8N  26.7W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  02/1800Z...DISSIPATED

$$
Forecaster Stewart

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