099
AWUS01 KWNH 261353
FFGMPD
FLZ000-GAZ000-ALZ000-261900-

Mesoscale Precipitation Discussion 1065
NWS Weather Prediction Center College Park MD
952 AM EDT Thu Sep 26 2024

Areas affected...Central Florida Panhandle into central Georgia

Concerning...Heavy rainfall...Flash flooding likely

Valid 261351Z - 261900Z

Summary...Repeating rounds of heavy rainfall featuring rates of
1-3"/hr will expand across the FL Panhandle and into the Southeast
today. Where the most pronounced training occurs, rainfall of 2-3"
is likely, with locally more than 5" possible across the central
FL Panhandle. Flash flooding is likely.

Discussion...The GOES-E WV imagery this morning clearly indicates
the impressive tropical moisture plume being channeled northward
from Hurricane Helene which is positioned in the southern Gulf of
Mexico. Downstream, deep moisture characterized by PWs measured by
GPS and regional 12Z soundings of 2-2.5" is funneling northward as
it gets squeezed east of a pronounced upper low positioned over
IL/IN. This impressive moisture will continue to be acted upon by
robust deep layer ascent through downstream mid-level divergence
between Helene and the upper low which will overlap with a
persistent jet streak centered over TN leaving favorable RRQ
diffluence from FL through western NC. A stationary front is
analyzed across the region resulting in locally enhanced
convergence and isentropic ascent as well. Despite abundant cloud
cover which will somewhat minimize the instability potential, the
impressive synoptic ascent into the deep moisture will continue to
support heavy rainfall through the afternoon.

The high-res CAMs are in pretty good agreement the next several
hours that heavy rain will focus along the stationary front and
expand/intensify downstream of Helene into the FL Panhandle. This
will likely result in dual maxima for rainfall through the aftn.

Along the front, 850mb winds surging to 30-45 kts will feature
increasing isentropic ascent and converge into the boundary
itself. This is reflected by increasing moisture transport vector
convergence, and Corfidi vectors that become increasingly parallel
to the mean flow and the front. This suggests persistent training
of rainfall rates which the HREF probabilities indicate have a
30-50% chance of exceeding 1"/hr. This could result in 2-3" of
rainfall and instances of flash flooding through the afternoon.

More significant flash flooding potential will gradually develop
across the central FL Panhandle, especially in the vicinity of the
Forgotten Coast. Here, 850mnb winds increasing to above 50 kts
will exceed the mean 0-6km wind, suggesting more broad enhancement
to the ascent. This will occur coincidentally with Corfidi vectors
becoming increasingly anti-parallel to the mean flow, suggesting
an enhanced backbuilding threat and training of rainfall rates
which the HRRR suggests could exceed 3"/hr (0.75-1"/15 mins). This
could produce locally as much as 5" of rain as reflected by 6-hr
HREF neighborhood probabilities, and this will occur atop soils
saturated from 24-hr rainfall that has been 4-8" in this region.
Any of the most intense rain rates will likely result in flash
flooding, with locally significant flash flooding possible in
urban areas or where training occurs atop the most primed soils.


Weiss

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...BMX...FFC...JAX...TAE...

ATTN...RFC...SERFC...NWC...

LAT...LON   33508431 33398358 32008269 30938294 29978357
            29798392 29498454 29378498 29518558 30218618
            31338605 32308558 33028496 33258477