Pronóstico de precipitación excesiva:
xcessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Wed Sep 16 2020
Day 1
Valid 12Z Wed Sep 16 2020 - 12Z Thu Sep 17 2020
...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS THE FAR
WESTERN FLORIDA PANHANDLE EXTENDING INTO PORTIONS OF THE ALABAMA
COAST AND SOUTHERN ALABAMA...
...HISTORIC AND CATASTROPHIC FLOODING ONGOING...
Historic and catastrophic flooding is ongoing across portion of
the Alabama coast into far western FL panhandle this morning as
the rain bands associated with Hurricane Sally continue to move
onshore. The hardest hit areas thus far are between Mobile Bay, AL
and west of Tallahassee, FL with radar estimates of 8 to 12 inches
which seemed to be underdone. Observations coming in from the
local offices (MOB/TAE) seem to support localized storm totals
approaching 15-20 inches thus far. With additional rainfall
expected, extreme, life-threatening flooding will continue through
much of the day.
The eye of Hurricane Sally is clearly evident from the KMOB radar.
Sally is located just SSE of Mobile, AL at this update and lifting
very slowly north. With cooling cloud tops noted by satellite
imagery around the main eyewall of Sally and above the convective
feeder bands, expect these intense rain rates to continue through
the next several hours. Based on radar estimates and gauge
reports, over 3-4+ inches per hour rain rates are possible within
the eyewall and feeder bands. This activity could linger for
hours. Therefore, additional rainfall amounts between Mobile Bay
and Pensacola will range between 8 to 12 inches (with locally
higher amounts very possible) through the afternoon hours. This
atop of the 8-16+ inches observed will continue to exacerbate the
ongoing extreme flooding along the coast and just inland. Storm
total along and just inland from the coast is still forecast to
range between 10-20 inches with isolated 35 inches possible.
There may very well be a very focused area of 20-30 inches in some
locations.
Eventually Hurricane Sally will move farther into southern AL and
turn to the northeast. The anomalously high precipitable water
values of 2.25-2.5+ inches will surge north. This combined with
improving instability should help maintain higher rain rates,
perhaps closer to 2 inches per hour. The QPF footprint should
remain east and north of the center of circulation as seen by the
enhanced low level convergence and upper level divergence
associated with the system. However, over time, the
thermodynamics will start to interact with the northern stream
trough/surface front shifting the heaviest QPF farther north and
east of the surface low. This transition will likely take shape
early Thursday morning as the rain expands into central portions
of GA. Rainfall from portions of southern/central AL into central
GA Wednesday afternoon through the overnight will range between 4
to 8 inches with isolated 12 inches possible. So, while ongoing
flooding continues closer to the coast, inland locations will
start to observe scattered to widespread flash flooding later in
the forecast period. Therefore, the Moderate Risk was maintained
and refined based on the latest NHC track and WPC QPF.
It should be noted that a very focused region of strong moisture
flux convergence will reside along the coast of the Carolinas
resulting in showers and thunderstorms. Heavy rain rates of over
2 inches per hour are possible with some training expected.
Therefore, a Marginal Risk area was expanded across this region.
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