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Tropical Storm MARIA


Tropical Storm Maria Discussion Number  50
NWS National Hurricane Center Miami FL       AL152017
1100 AM AST Thu Sep 28 2017

A burst of strong convection containing cloud top temperatures
colder than -70C has developed just east of the center since the
previous advisory. Based on the recent inner-core convective
development and a Dvorak current intensity estimate of 3.5/55 kt,
the initial intensity estimate is being maintained at 60 kt for this
advisory. Also, the last AMSU overpass around 0200 UTC indicated
that Maria has retained tropical characteristics based on a deep
warm core that extends from near the surface to above the 200 mb
level, accompanied by a warm anomaly of more than 2.5 deg C, present
in the upper-levels of the cyclone.

Maria is now situated on the north side of a strong deep-layer
ridge, and the initial motion estimate is now toward the east or
085/11 kt. The cyclone is expected to move in a general easterly
direction for the next 12-24 h along the northern edge of the
aforementioned ridge. Afterwards, Maria is forecast to get caught up
in west-southwesterly flow ahead of an approaching deep-layer trough
that is currently located over the Great Lakes region, causing the
cyclone to accelerate toward the east-northeast at forward speeds in
excess of 30 kt by 36 h. The new track guidance remains in excellent
agreement with cross-track differences of only about 60 nmi and
speed differences of just a couple of knots. As a result, little
change was made to the previous advisory track, and the new NHC
forecast lies down the middle of the guidance envelope, close to the
various consensus models.

Little change in intensity is forecast during the next 36 h or so
while Maria remains over SSTs of 26C-27C and the vertical shear is
less than 10 kt. By 36 h and beyond, Maria will be moving over
sub-25C SSTs, reaching 21 deg C water by 48 h. The colder water,
along with increasing wind shear and dry mid-level humidity values
of less than 40 percent, should induce some weakening. Maria is
expected to become extratropical by 72 h due to these unfavorable
dynamic and thermodynamic conditions. However, given the very cold
water that will exist beneath the cyclone, it is possible that Maria
could become extratropical as early as 48 h. The extratropical low
is expected 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 forecast remains in agreement with guidance
provided by the NOAA Ocean Prediction Center.


INIT  28/1500Z 36.8N  69.3W   60 KT  70 MPH
 12H  29/0000Z 36.9N  66.7W   55 KT  65 MPH
 24H  29/1200Z 37.4N  62.1W   55 KT  65 MPH
 36H  30/0000Z 38.8N  56.1W   55 KT  65 MPH
 48H  30/1200Z 41.3N  48.8W   55 KT  65 MPH
 72H  01/1200Z 47.9N  31.2W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  02/1200Z...DISSIPATED

Forecaster Stewart