Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Sat Oct 12 2024

Day 1
Valid 12Z 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...

Moisture and instability return northward into southern Florida
today which should result in deeper convection and the potential
for higher rainfall rates with PWs 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 deeper convective coverage
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 00z HREF guidance is 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.

Chenard


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 day 2 is a continuation of the threat on day 1 over
Southeast Florida. The overall thermodynamic ingredients remain
similar, however there is still spread with the mesoscale to
synoptic setup. The 00z GFS and ECMWF have trended quicker with the
weak wave and suggest the better organized convective risk Sunday
will now be offshore and over the Bahamas. However the Gem Reg and
some HREF members appear slower and focus more convection over
south FL.

The uncertainty in these details appears too large to go with
anything more than a Marginal risk at this time. Overall do tend to
think the flood risk Sunday is trending down compared to what it
looked like last night (given the trends noted in the ECMWF and
GFS), but favorable moisture and instability parameters suggest at
least a localized flash flood risk could persist.

Chenard


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.

Chenard


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