Sep 10, 2017 1300 UTC Day 1 Convective Outlook
Updated: Sun Sep 10 12:52:16 UTC 2017 (20170910 1300Z Day 1 shapefile | 20170910 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170910 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 8,429 4,812,035 Fort Lauderdale, FL...Pembroke Pines, FL...Hollywood, FL...Coral Springs, FL...Port St. Lucie, FL...
SLIGHT 20,733 7,211,744 Jacksonville, FL...Miami, FL...Hialeah, FL...Orlando, FL...West Palm Beach, FL...
MARGINAL 16,761 5,312,609 Tampa, FL...St. Petersburg, FL...Cape Coral, FL...Savannah, GA...Gainesville, FL...
Probabilistic Tornado Graphic
20170910 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
10 % 8,339 4,759,733 Fort Lauderdale, FL...Pembroke Pines, FL...Hollywood, FL...Coral Springs, FL...Port St. Lucie, FL...
5 % 20,975 7,382,530 Jacksonville, FL...Miami, FL...Hialeah, FL...Orlando, FL...West Palm Beach, FL...
2 % 16,752 5,394,355 Tampa, FL...St. Petersburg, FL...Cape Coral, FL...Savannah, GA...Gainesville, FL...
Probabilistic Damaging Wind Graphic
20170910 1300 UTC Day 1 Damaging Wind Probabilities Graphic
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.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 42,140 16,747,011 Jacksonville, FL...Miami, FL...Tampa, FL...St. Petersburg, FL...Hialeah, FL...
Probabilistic Large Hail Graphic
20170910 1300 UTC Day 1 Large Hail Probabilities Graphic
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.) Area Pop. 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...

   ...SUMMARY...
   Hurricane Irma's tornado risk will spread over much of the Florida
   Peninsula today and tonight.

   ...Synopsis...
   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. 

   ...Hurricane Irma...
   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
   south.

   ..Edwards/Broyles.. 09/10/2017

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