Mesoscale Discussion 1564
NWS Storm Prediction Center Norman OK
1019 AM CDT Fri Aug 25 2017
Areas affected...Texas Gulf Coast areas northeastward into far
southwestern Louisiana
Concerning...Severe potential...Watch likely
Valid 251519Z - 251815Z
Probability of Watch Issuance...80 percent
SUMMARY...Outer bands of convection associated with Hurricane Harvey
will continue to migrate toward the discussion area through the
afternoon, posing at least an isolated tornado threat. A Tornado
Watch may be needed at some point this afternoon.
DISCUSSION...Several bands of convection are migrating
west-northwestward toward the Texas Gulf Coast currently. One well
defined band located from near BPT southeastward to Louisiana
coastal waters should impact areas of southeast Texas over the next
several hours, although the tornado threat with this activity should
remain relatively low into the afternoon hours until kinematic
profiles increase attendant to the approaching Harvey. Another band
of convection over coastal waters southeast of PRX is also fairly
well defined, with a couple of mid-level mesocyclones noted via
WSR-88D imagery in individual cells with that band. Additionally,
more isolated convection was located outside of these bands over
open coastal waters, and these storms will also migrate
northwestward toward the discussion area throughout the afternoon
and into the evening hours.
Over time, as the circulation of Harvey approaches the coast,
low-level flow across the discussion area will veer to
easterly/southeasterly and kinematic fields will strengthen further,
resulting in a more appreciable tornado threat as a more unstable
airmass (1000-2000 J/kg MUCAPE) over coastal waters advances inland.
Pockets of surface insolation may also foster destabilization with
time.
While a tornado watch issuance is not immediately likely, one may be
needed over time as Harvey approaches land areas - more likely
during the afternoon hours.
..Cook/Darrow.. 08/25/2017
