Hurricane HANNA (Text)

Hurricane Hanna Discussion Number  11
NWS National Hurricane Center Miami FL       AL082020
1000 AM CDT Sat Jul 25 2020
NOAA Doppler radar data from Corpus Christi and Brownsville, Texas, 
along with reconnaissance data from the NOAA Hurricane Hunters 
indicate that Hanna has continued to strengthen this morning. A 
well-defined but fairly large 30-35-nmi-wide eye has formed and 
recent dropsonde data from the eye indicate that the central 
pressure has dropped to 978 mb. The aircraft measured a peak 700-mb 
flight-level wind speed of 77 kt, which equates to about 69 kt at 
the surface. During the past hour, Doppler velocities have sharply 
increased with numerous patches of 85-90 kt between 7000-8000 ft 
common in the northern eyewall. Although these values would 
typically correspond to surface winds of about 75 kt, the Doppler 
velocity are occurring in low reflectivity regions of 25-30 dBZ, so 
the full effect of those winds are likely not reaching the surface. 
This could be why the highest SFMR surface wind observed by the 
aircraft was only 63 kt. The initial intensity has been increased to 
70 kt, which is a blend of the aircraft flight-level, radar, and 
SFMR surface wind speed estimates.

The center position is a tad north of the recon fixes due to some 
southward tilt of the eye caused by northerly shear. This has 
resulted in a slower westward motion of 270/06 kt. The ridge to the 
north of the hurricane has been slowly building westward and 
southwestward based on upper-air data over the past 24 hours. This 
slow ridging pattern is expected to continue for the next 48 hours, 
resulting in  Hanna gradually turning toward the west-southwest by 
late this afternoon or evening, with landfall occurring in about 12 
h along south Texas coast. After landfall, Hanna should  continue 
its west-southwestward motion until dissipation over the mountainous 
terrain of northeastern Mexico in 48-60 h. The new NHC track 
forecast is similar to the previous advisory track, and lies close 
to the tightly packed consensus model guidance.
Although the deep-layer vertical wind shear is expected to remain 
out of the north-northwest to north at about 20 kt, the relatively 
large and stable eye, along with the expected convective vigor of 
the hurricane, could result in a little more strengthening just 
before landfall occurs. After landfall, rapid weakening of the wind 
field is expected. However, the weakening peak winds will have no 
negative effect on the likelihood for heavy rainfall or the 
possibility of isolated tornadoes developing.
Key Messages
1. Life-threatening storm surge is occurring along portions of the 
Texas coast from Port Mansfield to Sargent, where a Storm Surge 
Warning is in effect. Residents in these locations should follow 
advice given by local emergency officials.

2. Hurricane conditions are expected along the Texas coast from Port 
Mansfield to Mesquite Bay, where a Hurricane Warning is in effect.  
Tropical storm conditions are expected to first reach the coast 
within the warning area this morning.

3. Hanna is expected to produce heavy rains across portions of 
southern Texas and northeastern Mexico.  These rains could result in 
life-threatening flash flooding and isolated minor to moderate river 
INIT  25/1500Z 27.1N  96.3W   70 KT  80 MPH
 12H  26/0000Z 26.9N  97.6W   70 KT  80 MPH...INLAND
 24H  26/1200Z 26.4N  99.1W   45 KT  50 MPH...INLAND
 36H  27/0000Z 25.9N 100.6W   25 KT  30 MPH...INLAND
 48H  27/1200Z 25.3N 102.1W   15 KT  15 MPH...POST-TROP/REMNT LOW
 60H  28/0000Z...DISSIPATED
Forecaster Stewart

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Page last modified: Thursday, 31-Dec-2020 12:09:21 UTC