Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Miami Florida
826 PM EDT sun may 3 2015

Update...

For tonight a few fast moving showers moving from the northeast to
the southwest could affect the coastal areas from time to time. A
20 percent of showers is included in the forecast for the eastern
counties.

The forecast is still on track for the possibility of heavy rains
to occur in South Florida, especially the eastern half, beginning
Monday night. There is good model agreement in showing diffluence
aloft across South Florida during the day on Tuesday. All of this
along with the high moisture content will lead to very unstable
conditions along with the threat for heavy rainfall. However, it
is difficult to pinpoint the exact location where the heaviest
rains will occur.

The current hazards in effect are: high risk of rip currents for
all the Atlantic beaches and small craft advisories for the
offshore Gulf waters and all Atlantic waters. The high risk of rip
currents is being extended with this update until 00z Tuesday for
all Atlantic waters.

As Monday progresses, the rain chances will increase for the
Atlantic waters with showers possibly beginning to affect the East
Coast by evening.

&&

Previous discussion... /issued 728 PM EDT sun may 3 2015/

Aviation...
VFR will prevail with a windy easterly wind flow. Isolated showers
will continue possible Atlantic coast...but they will be few and
far between and fast moving and very brief. Gusty winds of around
25 knots expected during the day Monday. /Gregoria

Previous discussion... /issued 252 PM EDT sun may 3 2015/

Short term (tonight-Tuesday night)...
looks like the crazy weather of April will be extending into early
may, but more on that later. Currently, a mostly zonal flow pattern
persists across South Florida with a surface high pressure ridge
over the southeast states beginning to shift east into the Atlantic.
This has increased our pressure gradient with the surface wind
already gusting to over 20 knots along the East Coast with strong
rip currents at the beaches. This pattern will continue through
tonight. Monday will be a transitional day with the crazy weather
possible for Tuesday and Wednesday. On Monday, a weak southern
stream middle level trough will move into the far western Gulf of
Mexico and into the eastern Gulf Monday night. This along with the
surface flow becoming more southeasterly will begin to pull moisture
back to the north with forecast precipitable water climbing to around 1.4"
Monday afternoon and 1.8" Monday night and continuing through
Wednesday. The middle level trough will then reach somewhere near the
southern tip of the peninsula during Tuesday morning and then only
drift slowly to the northeast through Wednesday with high pwat's
remaining across the area while at the same time inducing low
pressure at the surface to the east over the southwest Bahamas.
Temperatures at the 500mb level are also forecast to be near
record cold for early may by Tuesday morning being in the range of
-11 to -12c. Model consensus has been very close to this solution
with slight differences in the position and timing of the two
troughs. There has also been good model agreement in showing
diffluence aloft across South Florida during the day on Tuesday.
All of this along with the high moisture content will lead to very
unstable conditions along with the threat for heavy rainfall.
There continues to be low confidence however in the exact rainfall
totals that could possibly unfold. Model consensus has also been
showing the deepest tropical moisture to remain offshore so for
now will continue to depict this set up. However, any little shift
to the west and the potential for possible flooding issues is
certainly there.

Long term (wednesday-sunday)...
on Wednesday and Thursday, the upper trough along with the surface
low will begin to lift northeast away from South Florida. However,
plenty of residual moisture will remain with rain chances remaining
high. By Friday, as the low intensifies off the Carolinas coast
drier air will begin to filter south into the area drying things out
for the latter part of the week into next weekend. By the end of the
week, the confidence in the forecast becomes very small. A massive
cut-off low will begin to develop across the western U.S. Which will
amplify a ridge across the eastern states to the north of the
trough. This will prevent it from moving much and it begins to
meander across the western Atlantic. The latest 12z run of the GFS
actually now shows the low drifting back to the southwest on
Saturday approaching the northeast coast of Florida. So even
though current thinking is for drier conditions, with the
uncertainty of the evolution of the trough will continue chance
for showers through the end of the forecast period.

Marine...
winds are forecast to slowly increase to 20 knots or just above
mainly across the off Gulf shore waters. Therefore a Small Craft
Advisory will be issued for tonight...starting at 00z for the off
shore Gulf waters.

With the combination of northeasterly winds in the 15 to 20
knot range across the Atlantic waters and a long period
northeasterly swell in the 2 to 4 foot range...hazardous seas to
near 7 feet are forecast across the Atlantic waters with a Small
Craft Advisory in effect through 00z Tuesday but this may need to be
extended.

There is a lot of uncertainty in the extended forecast given the
uncertainties outlined in the discussion above. So there could be
considerable changes to the wind and waves forecast in the
extended periods in the next few days.

&&

Preliminary point temps/pops...
West Palm Beach 71 82 73 76 / 20 20 60 70
Fort Lauderdale 72 81 73 79 / 20 20 60 70
Miami 71 82 71 80 / 20 20 60 70
Naples 63 88 68 84 / 0 10 10 60

&&

Mfl watches/warnings/advisories...
Florida...high rip current risk through Monday evening for flz168-172-173.

Am...Small Craft Advisory for hazardous seas until 8 PM EDT Monday
for amz650-651-670-671.

GM...Small Craft Advisory for winds until 8 am EDT Monday for gmz676.

&&

$$

Short term...71/je
long term....71/je
radar/aviation...57/dg

National Weather Service Glossary of Abbreviations