Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk
Area (sq. mi.)
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
SPC AC 101252
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Sun Sep 10 2017
Valid 101300Z - 111200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS NEAR THE
FLORIDA EAST COAST...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE OVER
MUCH OF THE FLORIDA PENINSULA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AND EXTENDING TO THE SOUTHERN SOUTH CAROLINA COAST...
Hurricane Irma's tornado risk will spread over much of the Florida
Peninsula today and tonight.
The mid/upper level pattern will remain characterized by ridging
wrapping around a slow-moving cyclone offshore from southern CA and
northern Baja. That ridging will extend to an elongated anticyclone
centered over the four Corners region, then northeastward through a
col over IA to a weak high over Lower MI. Meanwhile Hurricane Irma
(including its large, intense cyclone aloft) should continue to move
north-northwestward near the FL west coast after its current passage
across the Lower Keys. See NHC advisories for the latest tropical-
related warnings, watches and track/intensity guidance on Irma.
A quasistationary, residual surface frontal zone was analyzed
offshore the Carolinas, southwestward across northern FL then
west-southwestward over the northeastern Gulf. This boundary may
deform/shift somewhat northward over the coastal GA/Carolinas region
as the expansive wind field of Irma spreads over the region.
See SPC tornado watch 482 and mesoscale discussion 1637 for latest
near-term information in the tornado threat.
Tornado potential today should remain relatively maximized near the
east-central Fl coast, where a reasonably well-defined
marine/overland baroclinic gradient should persist through much of
the period. Surface temps 80s F in the relatively unmodified marine
air should support MLCAPE around 1500 J/kg, locally higher. Small
pockets or corridors of diffuse diurnal heating somewhat inland are
possible, but that prospect is uncertain given the extensive cloud
cover. In general, as the most favorable low-level shear shifts
northward across the outlook area, instability and buoyancy will
continue to decrease with westward extent, or inland from the
Atlantic with respect to the low-level trajectories. This is
related both to the lesser diabatic heating with proximity to the
large area of central dense overcast, and to more reduction of
theta-e by precip compared to the over-water marine-air source
region. Still, marginal thermodynamic profiles supporting MLCAPE up
to 500 J/kg are possible across the peninsula to near the west
coast, and a tornado cannot be ruled out from any relatively
sustained/discrete cell in that environment.
As the core region of Irma moves up the FL west coast and adjacent
waters today, the already expansive area of strong low-level winds
will continue to spread further up the east coast and inland areas
as well, largely in step with the center's translation vector.
Given favorable convective mode/coverage, increasing interaction of
that wind field with the residual frontal zone during the
middle/latter part of the period also may induce or maintain
mesoscale potential for supercells across parts of northeast FL and
immediate coastal areas of GA/SC tonight. That threat currently
appears more marginal/conditional than today over areas farther
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