Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
420 PM EDT Sat Oct 12 2024

Day 1
Valid 16Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Satellite and radar imagery was showing moisture and instability
returning northward into southern Florida which should result in
deeper convection and the potential for higher rainfall rates with
precipitable water values increasing towards 2.25". Meanwhile a
weak wave moving into the eastern Gulf of Mexico should result in
an uptick in low level flow and convergence. Thus expect we should
gradually see an uptick in coverage of deeper convection over the
Keys into south FL and the adjacent waters today into tonight.

The overall synoptic pattern still looks to favor slow moving
convective cells along and near the coastal convergence axis given
easterly low level flow and westerly upper level winds. Timing and
the CAPE distribution over land remain a bit uncertain. Some model
guidance wants to keep the better instability and convergence
offshore or over the Keys, while others shift these ingredients
more into the Southeast Fl coastal urban corridor. This decreases
confidence with regards to convective evolution.

The ingredients in place in the vicinity certainly support the
potential for a localized higher end flash flood event somewhere
within the southeast FL urban corridor today and/or tonight.
However the signal in the 12Z HREF QPF remained mixed, and overall
just not seeing enough in the probability fields to suggest we are
at Slight risk level coverage or confidence at this time.

Thus we will maintain the Marginal risk and continue to monitor
observational and model trends.

Bann


Day 2
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on Sunday is a continuation of today's threat over
Southeast Florida. The overall thermodynamic ingredients remain
similar, however there is still spread with the mesoscale to
synoptic setup. The 12/12Z GFS and 12/12Z ECMWF have trended
quicker with the weak wave and suggest the better organized
convective risk will now be offshore and over the Bahamas. However
the GEM and some HREF members are on the slower side and focus
more convection over south Florida.

The uncertainty in these details continues to be too large to go
with anything more than a Marginal risk at this time. Overall the
signals in the models suggest the flood risk on Sunday is trending
downward but lingering amounts of moisture and instability
parameters suggest at least a localized flash flood risk could
persist.

Bann


Day 3
Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024

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

Bann


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