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Hurricane Harvey Discussion Number  20
NWS National Hurricane Center Miami FL       AL092017
400 AM CDT Fri Aug 25 2017

The satellite presentation has improved during the past several
hours with an intermittent eye feature surrounded by a ring of very
deep convection. There are various cyclonically curved convective
bands primarily to the north of the eye and the outflow is fair.
NOAA and Air Force Hurricane Hunter planes penetrated the eye
various times during the past several hours, and the most
significant data were a flight-level peak wind of 103 knots, and a
peak SFMR surface wind of 88 kt. The central pressure dropped
to 967 mb. Based on these data, the initial intensity was adjusted
upward to 90 kt. Another reconnaissance plane will be in the eye of
Harvey shortly.

Since Harvey is embedded within light shear and moving over warm
waters, additional strengthening is anticipated before landfall in
about 24 hours.  Thereafter, gradual weakening is forecast but since
a good portion of the circulation will remain over water, the
weakening process could be slower than normal.

Radar and reconnaissance fixes indicate that Harvey is moving toward
the northwest or 320 degrees at 8 kt. The hurricane is on the
western edge of a persistent area of high pressure over the eastern
Gulf of Mexico, and this pattern will maintain the current hurricane
motion until landfall.  Once Harvey is inland over Texas, the
steering currents are forecast to collapse and the cyclone should
begin to meander, prolonging the flooding conditions for several
days. The track guidance between now and landfall is very consistent
and there is high confidence in the track forecast. After landfall,
the track models show large variability and the confidence is low.
In any case, NHC forecast depicts a slow moving tropical cyclone
near or over Texas for the next five days.

Once again, it is very critical that users not focus on the exact
forecast track of Harvey, since cycle-to-cycle adjustments 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 is expected 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 this morning, as tropical-storm-force winds will first
arrive in the hurricane and storm surge warning areas later today.

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 12
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. Devastating and life-threatening flooding is expected across the
middle and upper Texas coast from heavy rainfall of 15 to 25 inches,
with isolated amounts as high as 35 inches, from today through next
Wednesday. 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  25/0900Z 25.9N  95.4W   90 KT 105 MPH
 12H  25/1800Z 26.9N  96.3W  105 KT 120 MPH
 24H  26/0600Z 28.0N  97.1W  105 KT 120 MPH
 36H  26/1800Z 28.5N  97.4W   65 KT  75 MPH...INLAND
 48H  27/0600Z 28.5N  97.5W   60 KT  70 MPH...INLAND
 72H  28/0600Z 28.3N  97.0W   35 KT  40 MPH...INLAND
 96H  29/0600Z 28.5N  96.0W   35 KT  40 MPH...OVER WATER
120H  30/0600Z 29.5N  95.0W   35 KT  40 MPH...INLAND

$$
Forecaster Avila

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