SPC MD 1335

MD 1335 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR MIDDLE AND UPPER TEXAS COAST

Mesoscale Discussion 1335
NWS Storm Prediction Center Norman OK
0659 AM CDT Sat Jul 25 2020

Areas affected...Middle and Upper Texas Coast

Concerning...Severe potential...Watch possible 

Valid 251159Z - 251400Z

Probability of Watch Issuance...40 percent

SUMMARY...The tornado threat will gradually increase this morning as
tropical cyclone Hanna approaches the lower Texas Coast. A Tornado
Watch may be necessary later this morning for portions of the Texas
coast.

DISCUSSION...Low-level helicity continues to slowly increase this
morning across portions of the middle and upper Texas coast as
tropical cyclone Hanna approaches. On the northwest side of Hanna,
northerly shear has generally restricted the ability of feeder bands
to sustain themselves and penetrate inland. Recent radar and
satellite trends, however, suggests an uptick in convective vigor in
several bands to the east and southeast of Galveston, including
episodic areas of weak, broad low-level rotation embedded within the
more pronounced/robust updrafts to the southeast of Galveston. 

The commencement of diurnal heating to the north of the rain-filled
central dense overcast, combined with an increase in low-level
theta-e, should provide an increasingly favorable environment for
sustaining vigorous convection. At this time the most likely area
for this to occur will be across the northwest Gulf of Mexico, to
the north of the main core of Hanna. These storms will continue to
move to the west-northwest, impacting the middle and upper Texas
coast through the morning. With time, low-level wind fields should
strengthen in response to Hanna, resulting in an increasingly
supportive environment for tornadoes. Although a tornado watch is
not likely in the near term, one may be needed later this morning.

..Marsh/Edwards.. 07/25/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LCH...HGX...CRP...EWX...

LAT...LON   29719685 30299508 29979439 29299441 28869528 28359632
            27969679 28049753 28749770 29719685 

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from SPC Forecast Products http://www.spc.noaa.gov/products/md/md1335.html