545
FXUS62 KMFL 241813
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
213 PM EDT Tue Sep 24 2024

...New SHORT TERM, LONG TERM, MARINE, BEACHES...

.SHORT TERM...
(Rest of today through Wednesday)
Issued at 208 PM EDT Tue Sep 24 2024

Mesoanalysis this afternoon indicates that South Florida is fully
underway in the transition between the drier continental airmass
that has been in place across the region over the last several days
and the plume of deep tropical moisture now just to south. Taking a
look at the GOES-East water vapor imagery this afternoon depicts the
proverbial "knocking on the door" of the moisture envelope of
Tropical Storm Helene advecting slowly northward from the Florida
Keys and points southward. -3C to -4C 500mb temperatures aloft
indicate that mid- level ridging remains with us, hence the
continued presence of mid- lvl dry air and synoptic subsidence
over South Florida. This will result in one final afternoon of
continued suppression of widespread spatial convection. However
even with lackluster synoptic support, mesoscale boundaries such
as the Gulf sea-breeze will still produce enough ascent for a few
showers and isolated thunderstorms. Seasonably warm temperatures
can be expected with highs in the low 90s near the east coast and
mid 90s over Interior and SW Florida.

As the sprawling circulation and moisture envelope of Helene pushes
northward across the northwestern Caribbean Sea overnight, we
will start to feel the outer influences of the system. Deep
tropical moisture currently to the south of us is forecast to
advect northward, as evidenced by PWATs increasing over 2.2 inches
by Wednesday afternoon. Rain chances will increase from north to
south tonight (although likely confined to the waters and coastal
regions). HREF`s LPMM does hint at the potential of coastal
convergence taking place overnight along the east coast of South
Florida with localized pockets of heavy rainfall that could spark
a few localized flooding concerns.

A few outer bands from Helene will likely advect northwards across
the region on Wednesday with breaks of sunshine in between. Now
firmly in the outer fringes of the circulation, our forecast depicts
southeasterly winds will become increasingly breezy with gusts 25 to
30mph Wednesday afternoon. Marine and beach conditions will
gradually deteoriate throughout the day.

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 208 PM EDT Tue Sep 24 2024

The outer influences of Tropical Storm Helene will continue to
arrive across our region late on Wednesday as the center of the
system gradually lifts northwards across the Gulf of Mexico. A large
moisture envelope associated with the system and climatologically
significant precipitable water values will also advect into the
region during this time frame. The latest forecast models depict
potential precipitable water values of 2.3-2.5 inches which
correlates to near max values for the 25th and 26th of September.
Forecast models also indicate a long skinny CAPE sounding
indicative of ample warm cloud processes that supports heavy
rainfall potential. There has also been a consistent signal on the
European`s Extreme Forecast Index (EFI) and HREF`s LPMM for
coastal convergence along both coasts of South Florida. Given the
parameters specified above, the potential certainly remains for
heavy rainfall and localized flooding across portions of the area.
A Flood Watch has been issued for Collier, Glades, and Hendry
counties from Wednesday morning through Friday morning. In
general, rainfall amounts from late Wednesday through Friday
evening look to range from 2 to 4 inches across inland portions of
the region with the potential of higher rainfall totals in the
3-6 inch ballpark across both metro areas. A litany of products
continue for our Gulf coast locales outside of the Flood Watch, a
Tropical Storm and Storm Surge Watch remains in effect from Bonita
Beach to Flamingo. There is the potential of 2-4 feet of storm
surge across these areas with potentially locally 6+ in the most
vulnerable coastal locations given the large size of Helene and
shallow Florida shelf. Rough marine and boating conditions will be
felt across the entire region, with the greatest impacts realized
across our gulf waters. The probabilities of sustained tropical
storm force winds remain confined to coastal Collier throughout
the duration of Helene`s passage west of the region, however
forecast model guidance indicate a large and fairly robust
850-925mb wind field just above the surface. As the outer
feeder bands of Helene rotate across the region, there is the
potential for strong wind gusts of tropical storm force across the
entire region. A Wind Advisory may have to be considered for the
rest of the region not currently covered by tropical products.
Outside of the storm surge, flooding rain, and wind threat across
the region, the overall parameters for tropical tornadoes appears
to be limited by South Florida`s residence time in the northeast
quadrant. With the peak time of tropical tornadoes between 18Z-00z
due to the mixing of dry air and diurnal heating, the passage of
Helene closest to the region on Wednesday night may limit any
tornado potential to the coastal areas of Collier depending on
track. A second window for potential tornado genesis may
materialize across the Lake Okeechobee region during the
afternoon hours of Thursday as Helene moves further northward
across the eastern Gulf of Mexico. Given the cloud cover and
sprawling rain bands, temperatures should remain near
climatological norms. While it will not be a washout across the
region during this period, convective rain bands will bring
periods of gusty winds, blinding rainfall, and the potential of
localized flooding across our urban areas.

By late Thursday, the center of Helene will be well to the north of
the region with the attendant tail/trough situated across the
region. This "tail" of higher precipitable waters of 2.3-2.5" will
remain draped across our region as breezy southwesterly flow
continues across the region. Trailing bands of Helene will work
across the region on Friday with the potential of additional
localized flooding concerns. In addition, the continued breezy
southwesterly flow may result in an additional day of higher than
normal water level across the Gulf coast of South Florida. The
persistent tail/trough of Helene is forecast to remain situated
across the region this weekend which will maintain humidity across
the region as the boundary gradually begins to lift northwards.

High temperatures throughout the long term period will remain near
or slightly above climatological norms across South Florida with
highs in the upper 80s to low 90s.

&&

.AVIATION...
(18Z TAFS)
Issued at 132 PM EDT Tue Sep 24 2024

Mainly VFR conditions will prevail through the rest of the
afternoon and into the evening hours. Winds will remain out of the
ESE at 10 to 15 kts this afternoon. Scattered showers and storms
will form mostly over the interior sections this afternoon away
from the east coast terminals. Rain chances will begin to ramp up
overnight and into the day on Wednesday. Winds will increase out
of the SE early Wednesday morning and could gust to 25 kts as the
morning progresses.

&&

.MARINE...
Issued at 208 PM EDT Tue Sep 24 2024

Easterly winds will become fresh over the waters today as a
gradient strengthens to the north of Tropical Storm Helene in the
NW Caribbean. Winds and seas will then turn hazardous on
Wednesday as the system intensifies and lifts northward into the
SE GOM, with tropical storm conditions possible over the Gulf
waters and Gale conditions possible on the Atlantic waters on
Thursday. The chances of showers and thunderstorms will also
increase Wednesday into the late-week period.

&&

.BEACHES...
Issued at 208 PM EDT Tue Sep 24 2024

Minor coastal flooding will remain possible over the east coast
today but should generally be spotty as astronomical tides
decrease. Moderate to major coastal flooding can be expected over
the Gulf coast late Wednesday into Thursday as Tropical Storm Helene
strengthens and tracks through the SE Gulf of Mexico.

Strengthening onshore flow will result in an extended period of
high rip current risk over the east coast (likely through the
work week), with potentially hazardous surf developing over the
Palm Beaches in the mid-week period. Additionally hazardous beach
conditions look likely over the Gulf coast beaches starting
Thursday as surf increases in association with Tropical Storm
Helene.

&&

.PRELIMINARY POINT TEMPS/POPS...
Miami            81  89  79  89 /  60  80  90  80
West Kendall     78  89  79  90 /  60  80  90  80
Opa-Locka        80  90  79  90 /  50  80  90  80
Homestead        79  89  79  89 /  60  90  90  80
Fort Lauderdale  80  88  79  88 /  50  80  90  80
N Ft Lauderdale  80  89  79  90 /  50  80  80  80
Pembroke Pines   81  91  79  91 /  50  80  80  80
West Palm Beach  79  89  79  90 /  40  80  80  80
Boca Raton       80  89  79  90 /  50  70  80  80
Naples           79  90  78  87 /  40  90  90  90

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...Flood Watch from Wednesday morning through Friday morning for
     FLZ063-066-069-070.

     Storm Surge Watch for FLZ069-075.

     Tropical Storm Watch for FLZ069-075.

     High Rip Current Risk through Thursday evening for FLZ168-172-
     173.

AM...None.
GM...Tropical Storm Watch for GMZ656-657-676.

&&

$$

SHORT TERM...Hadi
LONG TERM....Hadi
AVIATION...CWC