SPC AC 090547
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1247 AM CDT Sat Sep 09 2017
Valid 101200Z - 111200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE EASTERN
FL PENINSULA AND FAR SOUTHEAST GA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE FL
PENINSULA AND GA/SC COAST...
Brief tornadoes are possible across portions of the Florida
Peninsula and coastal Georgia and South Carolina Sunday as Hurricane
Irma impacts the region.
Latest forecast track from the 03Z/Saturday advisory from the
National Hurricane Center takes the center of Hurricane Irma across
the western Florida Keys around 12Z Sunday and into the southwestern
FL Peninsula (in the Naples/Fort Myers FL vicinity) 00Z Monday. A
general north-northwestward motion is forecast to continue after
that, placing the center of system about 90 miles north-northwest of
Tampa Bay at 12Z Monday. Given that track, an environment supportive
of tropical cyclone tornadoes is anticipated along the eastern coast
of the FL Peninsula and into far southeast GA (discussed in more
Elsewhere, upper ridging will remain centered near the Four Corners
while an upper low off the southern CA coast drifts slightly
north-northwestward and deepens.
...Hurricane Irma: FL Peninsula and Coastal GA/SC...
The more westerly storm track will place a relatively higher threat
for tornadoes across eastern portions of the FL Peninsula than
anticipated by the previous outlook. Rainbands will likely be
impacting the entire peninsula at the start of the period, resulting
in a low threat for a few tornadoes along the length of the eastern
peninsula. Threat across the area will increase throughout the day
as the strong low/mid-level winds associated with Irma move over the
region. As expected, low-level shear will be more than sufficient
for tornadoes with instability and updraft strength/persistence
acting as the main limiting factors.
A comparatively higher tornado threat may develop in the vicinity of
the FL Space Coast during the afternoon. In this area, modest
heating between rainbands could align with very strong low/mid-level
flow, dewpoints in the mid 70s, and climatologically favorable
tropical cyclone orientation to support a locally higher tornado
potential. That being said, the threat for tropical cyclone-spawned
tornadoes is very track dependent and updates/changes to this
forecast may be needed in subsequent outlooks as the track changes.
Moisture will continue advecting northward into the region as
southerly/southeasterly flow around the eastern periphery of
previously mentioned the upper low persists. PW values will likely
be near 1.50" by 00Z Monday. This moisture coupled with orographic
effects and large-scale forcing for ascent provided by the upper low
will result in widely scattered thunderstorm development Sunday
afternoon/evening. Bulk shear supports a few strong storms but
overall severe coverage is currently expected to remain below 5%.
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