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Hurricane Maria Forecast Discussion


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Hurricane Maria Discussion Number  37
NWS National Hurricane Center Miami FL       AL152017
500 AM EDT Mon Sep 25 2017

A combination of conventional satellite imagery, scatterometer
data, and reports from a NOAA Hurricane Hunter aircraft indicate
that Maria is weakening and undergoing major changes in structure as
it encounters the cool water left by Hurricane Jose.  Satellite
imagery shows that the low-level center has become exposed to the
northwest of the remaining central convection, with some outer
convective banding remaining mainly in the eastern semicircle.  The
scatterometer and aircraft data suggests that the inner wind core
has collapsed, with no hurricane force winds occurring in the
western semicircle.  Based on the combination of these data, the
initial intensity is lowered to a possibly generous 70 kt, and the
initial and forecast wind radii have been significantly changed.

The initial motion is 355/6.  Maria is being steered by the flow
between a mid- to upper-level cyclone over the southeastern U.S. and
the subtropical ridge over the southwestern Atlantic.  A mid-level
ridge moving eastward across the northeastern U.S. will likely cause
Maria's forward motion to slow some more over the next couple of
days.  After that time, the mid-latitude westerlies are expected to
encroach on Maria, causing it to turn sharply to the east-
northeast and accelerate. The guidance is in good agreement on this
track scenario, and the new forecast track, which lies between the
ECMWF and the various consensus models, is an update of the
previous forecast.

The environment of cool sea surface temperatures and moderate shear
should keep Maria weakening.  However, it unclear just how fast it
will weaken, as the guidance has been generally forecasting a slower
weakening than has actually occurred.  The new intensity forecast
will follow the trend of the guidance and the previous forecast of
a gradual weakening, with Maria now forecast to weaken below
hurricane status after 36 h.  However, an alternate scenario is
that the cyclone continues weakening at a faster rate and thus
winds up weaker than the new intensity forecast.

Maria is a large cyclone, so even if it weakens to a tropical storm
and remains well offshore it is expected to bring tropical storm
conditions to portions of the North Carolina coast during the next
couple of days.


KEY MESSAGES:

1. Maria is forecast to continue moving northward, paralleling the
U.S. east coast, and it is likely that some direct impacts will
occur along portions of the coast beginning Tuesday.  A Tropical
Storm Warning has been issued for a portion of the coast of North
Carolina.

2. Storm surge flooding especially along the sound side of the
North Carolina Outer Banks is possible beginning Tuesday, and a
Storm Surge Watch has been issued for a portion of the North
Carolina Outer Banks.

3. Swells from Maria are increasing along the coast of the
southeastern United States and are expected to reach the Mid-
Atlantic coast today.  These swells will likely cause dangerous surf
and rip currents at beaches in these areas through much of the
week. For more information, please monitor information from your
local National Weather Service office at www.weather.gov.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 30.6N  73.0W   70 KT  80 MPH
 12H  25/1800Z 31.4N  73.2W   70 KT  80 MPH
 24H  26/0600Z 32.5N  73.3W   65 KT  75 MPH
 36H  26/1800Z 33.5N  73.3W   65 KT  75 MPH
 48H  27/0600Z 34.3N  73.2W   60 KT  70 MPH
 72H  28/0600Z 35.5N  72.0W   60 KT  70 MPH
 96H  29/0600Z 37.0N  66.5W   60 KT  70 MPH
120H  30/0600Z 40.0N  56.5W   60 KT  70 MPH

$$
Forecaster Beven

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