Aug 25 Friday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Fri Aug 25 2017

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane
Harvey, located over the western Gulf of Mexico.

1. A trough of low pressure extending from the eastern Gulf of Mexico
over central Florida continues to produce a large area of
disorganized cloudiness and thunderstorms. Although strong
upper-level winds could limit tropical cyclone formation, some
subtropical development is possible over the weekend or early next
week while the system moves northeastward over the western Atlantic
before it merges with a front. Regardless of development, very
heavy rain and flooding is possible over portions of southern and
central Florida during the next few days. Please refer to products
from your local National Weather Service office for more information
on this system.
* Formation chance through 48 hours…low…20 percent.
* Formation chance through 5 days…medium…40 percent.

Forecaster Brown

6 PM CDT POSITION AND INTENSITY UPDATE… …HARVEY BECOMES A CATEGORY FOUR HURRICANE… …SUSTAINED HURRICANE-FORCE WINDS SPREADING ONTO THE MIDDLE TEXAS COAST…

Hurricane Harvey Discussion Number 22
NWS National Hurricane Center Miami FL AL092017
400 PM CDT Fri Aug 25 2017
Despite its concentric eyewall structure, Harvey’s winds have
increased during the day. NOAA and Air Force Reserve Hurricane
Hunter planes have measured maximum flight-level winds of 129 kt
and SFMR winds to 102 kt. Based on these data, Harvey’s maximum
surface winds are estimated to be 110 kt. Harvey’s central pressure
has also continued to fall, and the latest estimate based on
dropsonde data is 941 mb.

Harvey still has not slowed down, and the initial estimate is
325/9 kt. Based on the forecast track, Harvey is expected to make
landfall along the middle Texas coast tonight. After that, the
track models insist that the hurricane will slow down considerably
during the next 24 hours, and it is likely to move very little
between 36 and 120 hours. In fact, there has been a somewhat
notable change in the guidance, with very few of the models showing
Harvey lifting out toward the northeast by the end of the 5-day
forecast period. As a result, the NHC track forecast has been
pulled back a bit and keeps Harvey near or just inland of the Texas
coast through the middle of next week. This slow motion only
exacerbates the heavy rainfall and flooding threat across southern
and southeastern Texas.

Harvey may continue to strengthen during the 6-12 hours it has
before landfall, but regardless it is expected to make landfall at
major hurricane strength. Gradual weakening is anticipated after
the center moves inland, but Harvey’s slow motion will keep a
significant portion of its circulation over water, which may slow
the weakening rate. As a result, the NHC intensity forecast leans
closer to the global model guidance instead of the statistical-
dynamical guidance, which seems to weaken Harvey too fast. Harvey
could maintain tropical storm strength for the entire 5-day
forecast period due to its proximity to the northwestern Gulf of
Mexico.

Key Messages:

1. Harvey will make landfall tonight, bringing life-threatening
storm surge, rainfall, and wind hazards to portions of the Texas
coast. Tropical-storm-force winds have moved onshore in portions of
the warning areas and conditions will continue to deteriorate as
the eye of Harvey approaches the middle Texas coast tonight.

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. Due to the slow motion of Harvey and a prolonged
period of onshore flow, water levels will remain elevated for
several days.

3. Catastrophic and life-threatening flooding is expected across the
middle and upper Texas coast from heavy rainfall of 15 to 30 inches,
with isolated amounts as high as 40 inches, through 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.

FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 27.5N 96.5W 110 KT 125 MPH
12H 26/0600Z 28.2N 97.0W 100 KT 115 MPH…INLAND
24H 26/1800Z 28.8N 97.5W 75 KT 85 MPH…INLAND
36H 27/0600Z 28.9N 97.8W 60 KT 70 MPH…INLAND
48H 27/1800Z 28.6N 97.8W 50 KT 60 MPH…INLAND
72H 28/1800Z 28.1N 96.9W 40 KT 45 MPH…INLAND
96H 29/1800Z 28.5N 96.0W 40 KT 45 MPH…OVER WATER
120H 30/1800Z 29.5N 95.5W 35 KT 40 MPH…INLAND

$$
Forecaster Berg