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Tropical Storm Harvey Discussion Number  16
NWS National Hurricane Center Miami FL       AL092017
1000 AM CDT Thu Aug 24 2017

Data from an Air Force Hurricane Hunter aircraft indicate that
Harvey is quickly strengthening, and the cyclone's structure has
improved markedly with the plane reporting a closed 15-20 n mi wide
eye.  The flight-level and SFMR winds support an intensity of 55 kt,
but one of the more notable measurements is the central pressure,
which has fallen to 982 mb.  With a pressure this low, it is likely
that the winds will respond and increase further, and Harvey
probably isn't too far from becoming a hurricane.

With Harvey now strengthening at a faster rate than indicated in
previous advisories, the intensity forecast has become quite
concerning.  Water vapor images indicate that the cyclone's outflow
is expanding--indicative of low shear--and Harvey will be moving
over a warm eddy of high oceanic heat content in the western Gulf of
Mexico in about 24 hours.  As a result of these conditions, several
intensity models, including the ICON intensity consensus, are now
explicit showing Harvey reaching major hurricane intensity.  What's
more astounding is that some of the SHIPS Rapid Intensification
indices are incredibly high.  As an example, the guidance is
indicating a 70 percent chance of Harvey's winds increasing by 45 kt
over the next 36 hours.  Based on this guidance, the NHC official
intensity forecast now calls for Harvey to reach major hurricane
strength by 36 hours, before it reaches the middle Texas coast.

Aircraft fixes indicate that Harvey has turned toward the north-
northwest, and the initial motion estimate is 340/9 kt.  A mid-
level high centered near Florida and the eastern Gulf of Mexico
should force Harvey toward the northwest later today, with that
trajectory continuing for the next couple of days.  By 48 hours,
the cyclone appears to get sandwiched between the same mid-level
high over the Gulf of Mexico and a larger high over the
Intermountain West, which will cause Harvey to slow down
considerably during its approach toward the Texas coast and then
potentially stall just inland on days 3 through 5.  Mainly based on
an adjustment of the initial position, the NHC forecast track has
been nudged northeastward on this cycle, but it still lies
relatively close to the TVCN multi-model consensus and the HFIP
Corrected Consensus Approach (HCCA).

It is critical that users not focus on the exact forecast track
of Harvey, since cycle-to-cycle adjustment are likely.  All
locations within the hurricane and storm surge warning areas should
be preparing for the possibility of major hurricane-force winds and
life-threatening storm surge.

Key Messages:

1. Harvey has intensified quickly this morning, and is now forecast
to be a major hurricane at landfall, bringing life-threatening storm
surge, rainfall, and wind hazards to portions of the Texas coast.
Preparations to protect life and property should be completed by
tonight, as tropical-storm-force winds will first arrive in the
hurricane and storm surge warning areas on Friday.

2. A Storm Surge Warning is in effect for much of the Texas coast.
Life-threatening storm surge flooding could reach heights of 6 to 10
feet above ground level at the coast between the north entrance of
the Padre Island National Seashore and Sargent. For a depiction of
areas at risk, see the Storm Surge Watch/Warning Graphic at
hurricanes.gov.

3. Life-threatening flooding is expected across much of the Texas
coast from heavy rainfall of 12 to 20 inches, with isolated amounts
as high as 30 inches, from Friday through early next week. Please
refer to products from your local National Weather Service office
and the NOAA Weather Prediction Center for more information on the
flooding hazard.

4. The Potential Storm Surge Flooding Map is available on the NHC
website. This product depicts a reasonable worst-case scenario -
the amount of inundation that has a 10 percent chance of being
exceeded at each individual location. This map best represents
the flooding potential in those locations within the watch and
warning areas.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 24.0N  93.3W   55 KT  65 MPH
 12H  25/0000Z 24.9N  94.2W   70 KT  80 MPH
 24H  25/1200Z 26.0N  95.3W   90 KT 105 MPH
 36H  26/0000Z 27.3N  96.3W  100 KT 115 MPH
 48H  26/1200Z 28.3N  97.0W   95 KT 110 MPH...INLAND
 72H  27/1200Z 29.0N  97.7W   40 KT  45 MPH...INLAND
 96H  28/1200Z 28.5N  97.5W   35 KT  40 MPH...INLAND
120H  29/1200Z 28.5N  96.5W   30 KT  35 MPH...INLAND

$$
Forecaster Berg

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