Aug 28 Monday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Mon Aug 28 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Harvey, located near Matagorda Bay, Texas.

The National Hurricane Center is issuing advisories on Potential
Tropical Cyclone Ten, located off the southeast U.S. coast.
* Formation chance through 48 hours…high…90 percent.
* Formation chance through 5 days…high…90 percent.

1. A tropical wave located near the coast of western Africa is
producing a large area of showers and thunderstorms. Environmental
conditions are forecast to be conducive for gradual development of
this system while it moves westward at 15 to 20 mph over the
tropical Atlantic during the next several days.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…medium…50 percent.

Public Advisories on Potential Tropical Cyclone Ten are issued under
WMO header WTNT35 KNHC and under AWIPS header MIATCPAT5.
Forecast/Advisories on Potential Tropical Cyclone Ten are issued
under WMO header WTNT25 KNHC and under AWIPS header MIATCMAT5.

Forecaster Zelinsky/Landsea

 

DISTURBANCE REMAINING STATIONARY OFF THE SOUTHEAST U.S. COAST

Potential Tropical Cyclone Ten Discussion Number 3
NWS National Hurricane Center Miami FL AL102017
500 AM EDT Mon Aug 28 2017

Potential Tropical Cyclone Ten continues to lack a well-defined
center, as shown in the coastal stations, buoys, and ASCAT
scatterometer passes. Moreover, the convection – while deep – is
now strung out linearly from northeast to southwest, more
reminiscent of a front or trough. Thus it does not appear that
genesis into a tropical cyclone is imminent. Observations from
buoys and the ASCAT passes indicate that the peak winds remain
about 30 kt.

While the disturbance has plenty of warm water and moist air
available, it’s being sheared by strong upper-level westerlies.
The shear may lessen slightly over the next day or so, allowing
a short window of opportunity for the system to undergo genesis and
some intensification. But in about 36-48 hr, the shear should go
back up as the system reaches cooler SSTs, likely limiting the
intensification as a tropical cyclone. At about the same time, the
system should transform into an extratropical cyclone and further
develop via baroclinic forcing. The intensity forecast shows a
slightly delayed genesis and more gradual intensification through
24 hr compared to the previous advisory and about the same
thereafter. This forecast is based upon a blend of the
statistical, hurricane-mesoscale, and global models.

The disturbance is officially shown as stationary, but this is an
educated guess without a well-defined center being present. After
meandering for another 12 hr or so, the system should consolidate
and begin accelerating off toward the northeast. The mesoscale and
global guidance shows higher uncertainty than usual in the 12-36 hr
time frame and lower uncertainty for the 72 hr and beyond
forecasts, likely because of the variability in the models of where
and when a well-defined center forms. The official track forecast
is very similar to the previous one.

The track, intensity, and size forecasts for 48 hr and beyond are
based upon guidance provided by the Ocean Prediction Center. Note
that even though potential impacts from this system’s winds could
occur within the 36 hr time frame for a Tropical Storm Warning,
because the intensity forecast is for a low-end tropical storm and
the winds are all over the eastern semicircle, the threat of
coastal tropical storm winds remains possible but low. Thus the
Tropical Storm Watch for portions of South Carolina and North
Carolina are retained at this time.

FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 30.3N 81.0W 30 KT 35 MPH…POTENTIAL TROP CYCLONE
12H 28/1800Z 31.1N 80.9W 30 KT 35 MPH
24H 29/0600Z 32.9N 79.2W 35 KT 40 MPH…TROPICAL CYCLONE
36H 29/1800Z 35.0N 76.1W 40 KT 45 MPH…INLAND
48H 30/0600Z 37.5N 72.0W 50 KT 60 MPH…POST-TROP/EXTRATROP
72H 31/0600Z 41.0N 62.0W 60 KT 70 MPH…POST-TROP/EXTRATROP
96H 01/0600Z 44.0N 51.5W 55 KT 65 MPH…POST-TROP/EXTRATROP
120H 02/0600Z 48.5N 37.0W 40 KT 45 MPH…POST-TROP/EXTRATROP

$$
Forecaster Landsea

 

LIFE-THREATENING FLOODING CONTINUES OVER SOUTHEASTERN TEXAS… …DO NOT ATTEMPT TO TRAVEL IN THE AFFECTED AREAS IF YOU ARE IN A SAFE PLACE AND DO NOT DRIVE INTO FLOODED ROADWAYS

Tropical Storm Harvey Discussion Number 32
NWS National Hurricane Center Miami FL AL092017
400 AM CDT Mon Aug 28 2017

Harvey is producing intense convection in bands over the eastern
semicircle of the circulation. This is resulting in the
continuation of very heavy rains and life-threatening flash flooding
over southeastern Texas and southwestern Louisiana. There have
been reports of 2-day rainfall totals of close to 30 inches in the
Greater Houston area. With the additional rains that are expected
over the next several days, rainfall totals could reach 50 inches in
some locations, which would be historic for the area.

The initial intensity estimate remains 35 kt, based on the
assumption that winds of this strength are occuring in some of the
stronger bands. Since Harvey is forecast to be back over water just
offshore of the coast during the next couple of days, there is some
potential for restrengthening. Significant strengthening is not
anticipated, however, due to the system’s lack of an inner core and
strong southwesterly shear associated with an upper-level trough
over Texas.

Radar and surface observations indicate that the center is moving
slowly southeastward, or 130/3 kt. A mid-level trough dropping
into the Ohio Valley should cause Harvey to turn toward the east
and northeast and move back over land in a couple of days. The
official track forecast remains close to the dynamical model
consensus.

Although the tropical storm warning may need to be extended eastward
along the upper Texas and southwest Louisiana coasts later this
morning, heavy rainfall and life-threatening flooding continue to be
the primary threats.

Key Messages:

1. Ongoing catastrophic and life-threatening flooding will continue
across southeastern Texas. Additional rainfall accumulations of 15
to 25 inches are expected across the upper Texas coast, with
isolated storm totals as high as 50 inches. Please heed the advice
of local officials. Do not attempt to travel if you are in a safe
place, and do not drive into flooded roadways. Refer to products
from your local National Weather Service office and the NOAA Weather
Prediction Center for more information on the flooding hazard. A
summary of rainfall totals compiled by the Weather Prediction Center
can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html

2. The flood threat is spreading farther east into Louisiana.
Additional rainfall amounts of 15 to 25 inches are expected in
southwestern Louisiana, with rainfall amounts of 5 to 15 inches
expected in south-central Louisiana. Please heed the advice of
local officials and refer to products from your local National
Weather Service office and the NOAA Weather Prediction Center for
more information on the flooding hazard in these areas.

FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 28.6N 96.3W 35 KT 40 MPH
12H 28/1800Z 28.4N 96.0W 35 KT 40 MPH…OVER WATER
24H 29/0600Z 28.1N 95.6W 35 KT 40 MPH…OVER WATER
36H 29/1800Z 28.3N 95.2W 40 KT 45 MPH…OVER WATER
48H 30/0600Z 29.0N 94.7W 40 KT 45 MPH…OVER WATER
72H 31/0600Z 31.0N 93.9W 35 KT 40 MPH…INLAND
96H 01/0600Z 33.4N 92.5W 30 KT 35 MPH…INLAND
120H 02/0600Z 35.0N 90.5W 25 KT 30 MPH…INLAND

$$
Forecaster Pasch