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Hurricane Maria Discussion Number  30
NWS National Hurricane Center Miami FL       AL152017
1100 AM EDT Sat Sep 23 2017

Data from this morning's Air Force Hurricane Hunter flight suggests
that Maria's maximum winds may be decreasing a bit--a trend which
was noted in the previous advisory package.  The plane measured a
maximum 700-mb flight level wind of 102 kt and SFMR winds as high
as 85 kt, neither of which supports an intensity of 105 kt.  The
initial intensity is therefore conservatively lowered to 100 kt.

Maria is now located between a mid-level high centered near Bermuda
and a cut-off low over the northeastern Gulf of Mexico, both of
which are steering the hurricane north-northwestward, or 340/7 kt.
Maria should turn northward between these two features beginning in
about 12 hours, but its forward motion is likely to be impeded in a
couple of days by ridging developing over the northeastern United
States.  As a result, the hurricane's forward speed will decrease
to 5 kt or less from day 2 and beyond.  The track guidance has
continued to trend toward slower and farther westward solutions,
and as we had foreshadowed in previous discussions, an additional
westward adjustment to the new NHC track forecast was required on
this cycle.  The updated forecast is between the GFS and ECMWF
solutions and close to the consensus aids and HCCA through day 3.
After that time, the new forecast is slower and southwest of the
consensus aids, but still not quite as far west as the GFS, ECMWF,
and UKMET solutions.

Based on various analyses, the southwesterly shear over Maria has
decreased since yesterday, and it appears to remain relatively low
for the next 2 days or so.  Maria will be moving over very warm
waters during that time, although the depth of the warm pool does
decrease, and Maria's slower motion could increase the effects of
colder upwelled water.  After 48 hours, vertical shear is forecast
to increase again, and a critical part of the intensity forecast
will be whether or not Maria moves over the cold wake left behind by
Jose.  The recent westward shifts in the forecast track make it more
likely that Maria would avoid the cold wake and move over the warmer
Gulf Stream waters.  Since the environment may not be as hostile as
the dynamical models are assuming, the NHC intensity forecast is a
little above the intensity consensus for much of the forecast
period.

To increase the sampling of the environment upstream and north of
Maria, supplemental 0600/1800 UTC upper-air soundings are scheduled
to begin from the eastern and southeastern United States this
afternoon.  In addition, NOAA G-IV missions are scheduled to begin
sampling the environment around Maria on Sunday.


KEY MESSAGES:

1. Maria's forecast track has shifted closer to the U.S. east coast,
and it is becoming increasingly likely that some direct impacts will
occur along portions of the coast next week.  Interests along the
coast of the Carolinas and the Mid-Atlantic should monitor the
progress of Maria, as tropical storm or hurricane watches may be
needed for part of this area on Sunday.

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

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 25.4N  72.3W  100 KT 115 MPH
 12H  24/0000Z 26.7N  72.6W  105 KT 120 MPH
 24H  24/1200Z 28.3N  73.0W  105 KT 120 MPH
 36H  25/0000Z 29.5N  73.3W  100 KT 115 MPH
 48H  25/1200Z 30.5N  73.4W   95 KT 110 MPH
 72H  26/1200Z 32.1N  73.4W   85 KT 100 MPH
 96H  27/1200Z 33.5N  73.5W   75 KT  85 MPH
120H  28/1200Z 34.5N  72.5W   65 KT  75 MPH

$$
Forecaster Berg

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