Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
852 AM EDT Fri Oct 16 2026

Day 1
Valid 12Z Fri Oct 16 2026 - 12Z Sat Oct 17 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CENTRAL/SOUTH FLORIDA...

Locally heavy to potentially excessive rainfall will be possible
today across portions of the central and southern Florida peninsula
given the moist and unstable airmass in place and expected slow
storm motion. The Marginal Risk continues to highlight the area
where the HREF and REFS both generally show higher (greater than 50
percent) probabilities for accumulations exceeding 3 inches.

Bann


Day 2
Valid 12Z Sat Oct 17 2026 - 12Z Sun Oct 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS
OF THE FLORIDA EAST COAST...

Showers and thunderstorms...some capable of producing localized
downpours that result in flooding...should develop along and ahead
of a cold front making its way southward across the Florida
peninsula on Saturday. Both the HreF/RRFS guidance develop low-end
probabilities of flash flood guidance near the front during the
time of maximum diurnal heating. Rainfall rates of locally 2-3"/hr
within any convective cores suggest isolated totals of 4-6" are
very much plausible. The previous MRGL risk was maintained with no
adjustment.

Bann


Day 3
Valid 12Z Sun Oct 18 2026 - 12Z Mon Oct 19 2026

...MARGINAL RISKS OF EXCESSIVE RAINFALL EXIST FOR THE GOLD COAST OF
FLORIDA SUNDAY...

...FL Gold Coast...
A well defined cold front is expected to press southward before
stalling south of Florida on Monday. Moderate to strong post-
frontal on-shore flow Low level flow will focus moisture flux
convergence in proximity of the front. Strong boundary layer
convergence maxima likely along the east central coast of Florida,
which would be strongest overnight will support potential for
locally heavy rains from well defined rain bands that may train for
periods early Sunday. There has been a subtle southward shift in
the placement of the rainfall compared with previous model
runs...but spaghetti plots from the ECMWF Ensembles and the GEFS
ensembles still indicate that some potential lingers for 3+ inch
amounts during the period. Consequently...shrunk the Marginal risk
area somewhat but did not remove it.

Bann


Day 4 and Day 5
Valid 12Z Mon Oct 19 2026 - 12Z Wed Oct 21 2026

...MARGINAL RISKS OF EXCESSIVE RAINFALL EXIST FOR PORTIONS OF THE
EAST COAST MONDAY INTO WEDNESDAY MORNING...

...Eastern NC/Southeast VA...
The guidance is trending more towards an occluded low not far off
the Southeast Coast, which could have some interior convection as
-18C air at 500 hPa moves over 28-29C sea surface temperatures
during the short range period and perhaps a convective comma
head/TROWAL which feeds off additional instability from the
western subtropical North Atlantic. Wet solutions are now shown
on the 00z Canadian and 00z ECMWF, with the 00z GFS barely off the
coast with its heavy rain signal Monday/Monday night before it
ejects the cyclone northeast due to a slightly stronger shortwave
moving through Atlantic Canada. The 00z ECMWF AIFS and 00z AIGFS
are supportive of their control/operational runs respectively.
Since support appears to be slowly increasing and spread generally
decreasing. left the Marginal Risk from continuity for coastal
NC/VA for Monday/Monday night and introduced a new MRGL for a
similar locale Tuesday/Tuesday night.

...Southwest...
There was consideration for a Marginal Risk for portions of
southeast and central AZ to the southeast and eventually east of a
deep layer cyclone/"outside slider" moving west of CA, but the
atmosphere didn't appear to be sufficiently saturated with 0.75-1"
precipitable water values in an environment with 5640-5670
decameter 1000-500 hPa thickness. MU CAPE also appears skimpy,
with only small pockets of 250 J/kg forecast by the 00z GFS and 100
J/kg by the 00z ECMWF. While the threat for flash flooding/
excessive rainfall may be non-zero, did not feel it was up to the
Marginal Risk threshold so left risk areas out, for the time being.
This can be re-evaluated in later cycles.

Roth


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