698
FOUS30 KWBC 050058
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Fri Oct 4 2024

Day 1
Valid 01Z Sat Oct 05 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Pereira

Day 2
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

A lingering coastal trough will remain parked off the South TX
coast with a prevailing northeasterly flow pattern situated from
South Matagorda Bay down into the Lower RGV with elevated PWATs
situated along the coastal plain. The combination of marginal
instability and improving deep layer moisture will present an
opportunity for scattered to numerous convective cells pivoting
onshore from the adjacent Gulf. Current neighborhood probs for >3"
are very elevated (60-80%) over the course the D2 time frame with
a majority of the precip falling in the first 6-8 hrs of the period
before slowly waning. The 12-15 hour period from the end of D1
through the first half of D2 is signaling locally upwards of 5-7"
in the hardest hit locations with the accumulating factor of
precip from period to period relating to the flash flood chances as
we move into D2. In coordination with the local WFO BRO in South
TX, a targeted MRGL risk was added across the coastal portions of
the region, including parts of Kenedy, Willacy and Cameron
counties.

Kleebauer

Day 3
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTH FLORIDA PENINSULA...

A broad expanse of elevated moisture within a disheveled tropical
wave/trough axis over the Gulf will migrate eastward towards the FL
Peninsula by later Sunday with an increasing heavy rain threat
situated over the Southwest coast of FL, expanding eastward over
the Everglades and eventually the metro corridor in Southeast FL.
Recent trends within both deterministic and ensembles have
increased areal coverage of 2+" precip potential to include now
both coasts within South FL with the precip maximum creeping closer
to 4" locally as we move forward with time. The prospects of flash
flooding will only look to increase so long as the trend remains
and the CAMs begin noting heavier pockets of precip as we introduce
better convectively allowing physics into the setup. Recent ECMWF
AIFS ML output pinpoints the introduction of heavier rain across
the above area allowing for heightened confidence for the threat.
FFG indices will remain high just given the regions impacted, but
the urban setting will still be present for the greatest expected
impacts during the period. The previous MRGL risk was maintained,
but in coordination with the Miami WFO, the risk was expanded to
include the metro corridor on the opposite coast up to just south
of Lake Okeechobee.

Kleebauer

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt