Aug 29 Tuesday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Tue Aug 29 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Harvey, located just offshore of the middle Texas coast.

The National Hurricane Center is issuing advisories on Potential
Tropical Cyclone Ten, located just offshore of the North Carolina
coast.
* Formation chance through 48 hours…medium…40 percent.
* Formation chance through 5 days…medium…40 percent.

1. Showers and thunderstorms associated with a low pressure area near
the Cabo Verde Islands have become better organized since yesterday.
Environmental conditions are conducive for development, and a
tropical depression is expected to form in 2 or 3 days over the
eastern Atlantic. The low is forecast to move generally
west-northwest at 15 to 20 mph over the tropical Atlantic during the
next several days. Heavy rain is possible over portions of the Cabo
Verde Islands through Wednesday.
* Formation chance through 48 hours…high…70 percent.
* Formation chance through 5 days…high…90 percent.

Forecaster Blake

 

DISTURBANCE MOVING NORTHEASTWARD PAST CAPE FEAR

Potential Tropical Cyclone Ten Discussion Number 7
NWS National Hurricane Center Miami FL AL102017
500 AM EDT Tue Aug 29 2017

The disturbance has developed a center that has been trackable
this evening though it is still not well-defined, since it
appears to be considerably elongated northeast-southwest. The
disturbance continues to display very cold, but extremely asymmetric
deep convection with all of the thunderstorm activity east of the
center due to strong vertical shear. Moreover, the convection is
showing no identifiable banding features. So the system is not yet
a tropical cyclone. Regardless of the label we use to describe this
hybrid system, maximum winds are around 35 kt based upon a Dvorak
classification from TAFB and observed winds just below that from
the NDBC Buoy 41013.

The initial motion of the disturbance is northeast at a faster rate
of about 10 kt. Continued acceleration is expected during the next
couple of days as a mid- to upper-level trough over the Great Lakes
moves closer to the system. The NHC forecast track takes the
disturbance across the North Carolina coastline today. By tonight,
the cyclone is forecast to move offshore and accelerate over the
Atlantic in the mid-latitude westerlies. The NHC track forecast lies
near the middle of the guidance envelope and is not substantially
changed from the previous advisory.

Given the poor organization of the disturbance and the strong wind
shear environment that it is embedded within, the chances of this
disturbance becoming a tropical cyclone have decreased to about a
coin flip. Nonetheless, the potential impacts of tropical-storm-
force winds across portions of North Carolina are likely today even
if the system does not become a tropical cyclone. The system is
expected to become extratropical in 24 hours or less when it
interacts with the aforementioned mid- to upper-level trough.
Significant strengthening as an extratropical cyclone is forecast
for a couple of days due to baroclinic forcing. No significant
change has been made to the NHC intensity forecast.

The track, intensity, and wind radii forecasts from 24 to 120 h are
based on guidance provided by NOAA’s Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT 29/0900Z 33.5N 78.5W 35 KT 40 MPH…POTENTIAL TROP CYCLONE
12H 29/1800Z 35.4N 76.0W 40 KT 45 MPH
24H 30/0600Z 38.0N 71.5W 50 KT 60 MPH…POST-TROP/EXTRATROP
36H 30/1800Z 39.5N 66.5W 60 KT 70 MPH…POST-TROP/EXTRATROP
48H 31/0600Z 41.0N 61.0W 70 KT 80 MPH…POST-TROP/EXTRATROP
72H 01/0600Z 44.5N 50.0W 50 KT 60 MPH…POST-TROP/EXTRATROP
96H 02/0600Z 50.0N 33.0W 40 KT 45 MPH…POST-TROP/EXTRATROP
120H 03/0600Z 55.0N 19.0W 30 KT 35 MPH…POST-TROP/EXTRATROP

$$
Forecaster Landsea

 

CONTINUED HEAVY RAINFALL TODAY IS EXPECTED TO WORSEN THE FLOOD SITUATION IN SOUTHEASTERN TEXAS AND SOUTHWESTERN LOUISIANA… …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 36
NWS National Hurricane Center Miami FL AL092017
400 AM CDT Tue Aug 29 2017

Heavy rains continue to spread over the Houston area and other
locations in southeastern Texas and southern Louisiana,
exacerbating what is already a catastrophic flood event. Rainfall
totals exceeding 40 inches have been observed at several locations
in the Greater Houston area and southeastern Texas. Storm totals
could reach 50 inches in some locations, which would be historic for
the area.

The center of Harvey is moving slowly over the waters of the
extreme northwestern Gulf of Mexico, and there continues to be
essentially no deep convection near that center. The current
intensity is estimated to still be 40 kt based on surface
observations from buoys and land stations. Given the lack of
central convection and strong south-southwesterly shear over the
system, significant restrengthening is not anticipated before the
center crosses the coast again within 36 hours or so. Gradual
weakening will occur after landfall.

Harvey has turned from an east-southeastward to an eastward
heading and the initial motion is now about 100/3 kt. The storm
should turn northeastward to north-northeastward over the next
couple of days as a ridge to the northwest of the system
weakens and Harvey is steered around the western side of a ridge
to the east. Some further eastward adjustments to the official
track forecast were made, following the latest model consensus
forecasts. However, it is important not to focus on the exact
forecast track since the main threat from Harvey, heavy rain and
flooding, can and will occur well removed from the track of the
center.

Key Messages:

1. Ongoing catastrophic and life-threatening flooding will continue
across southeastern Texas. Additional rainfall accumulations of 7
to 13 inches are expected across the upper Texas coast into
southwestern Louisiana, 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 has spread farther east into Louisiana.
Additional rainfall amounts of 5 to 15 inches are expected in
south-central Louisiana. Rainfall amounts of 5 to 10 inches are
expected in southeast Louisiana and coastal Mississippi and
Alabama. 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 29/0900Z 28.1N 94.8W 40 KT 45 MPH
12H 29/1800Z 28.3N 94.5W 40 KT 45 MPH
24H 30/0600Z 28.8N 93.9W 40 KT 45 MPH
36H 30/1800Z 29.9N 93.4W 40 KT 45 MPH…INLAND
48H 31/0600Z 31.1N 92.7W 35 KT 40 MPH…INLAND
72H 01/0600Z 33.7N 90.7W 30 KT 35 MPH…INLAND
96H 02/0600Z 36.0N 87.5W 25 KT 30 MPH…POST-TROP/INLAND
120H 03/0600Z 37.5N 83.5W 20 KT 25 MPH…POST-TROP/INLAND

$$
Forecaster Pasch