Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Miami Florida
940 am EDT Thursday Sep 3 2015
adjusted near term grids to reflect current conditions and probability of precipitation
through the day based on 12z radiosonde observation analysis and mesoscale guidance.
No significant changes needed. Precipitable waters near seasonal averages...weak
mllrs and warm temperatures aloft should preclude much in the way of
organized convection...but isolated strong winds gusts over the
interior cant be ruled out.
Previous discussion... /issued 740 am EDT Thursday Sep 3 2015/
VFR conditions will prevail through the period...with the
exception of brief...possibly significant...restrictions this
afternoon in scattered thunderstorms and rain. Light winds this morning...then
onshore /ESE all but kapf...W/ winds around 10 knots this
afternoon...becoming calm after sunset.
Previous discussion... /issued 354 am EDT Thursday Sep 3 2015/
weak low pressure to the northeast will drift to the south,
ending up to the east of the region. This will keep the winds
generally out of the west to northwest through midday Saturday.
This will allow the Gulf sea breeze to penetrate further into the
interior, and possibly not collide with the Atlantic sea breeze
until it reaches somewhere just to the west of the Southeast
Florida metropolitan area. This will allow the convective development to
be mainly in the interior and move closer to the East Coast each
day. One of the determining factors will be how far the Atlantic
sea breeze is able to penetrate to the west.
By Saturday afternoon, the low pressure will have moved south
enough to turn the wind more to the north perhaps even to the
north northeast over the Atlantic waters, and the eastern portion
of the County Warning Area. Another, weak low pressure area will attempt to form
over South Florida. This will keep the wind out of the northeast
over the Gulf waters and the western areas of the County Warning Area. The models
show the convergence area over southwest Florida for Saturday
On Sunday, the pressure gradient over South Florida will weaken,
but the winds will remain out of the north. A trough at 500mb will
begin to move into the area. This will create some additional
dynamics. This will cause a more widespread likelihood of probability of precipitation for
This upper level trough will weaken through the middle of the
week. However it will continue to provide the additional dynamics
to allow more widespread coverage of showers and thunderstorms
across South Florida.
For today, there will be convective development forming in the
western interior along the Gulf sea breeze and progressing slowly
to the east, which is supported by the short range models. Some of
these models have the convection making it further east than
others. However, with likely probability of precipitation over most of the interior, most
of the solutions of the models will be adequately covered.
Looking at NAM model soundings, today looks as though conditions
will vary across the area. Of course the better dynamics look to
be in the interior. Precipitable waters in the sounding, over the Atlantic
coast, look to be just under 2 inches. Whereas the interior has
around 2.25 inches. The 500 mb temperatures are not that
impressive, coming in around -6c. The freezing level is around
15000ft today. This would put the 50 dbz core needed for large
hail up to between 39000 and 40000 feet. The ncape values will vary
from around .1 along the coast, to .22 in the interior. Thus, some
hail will be possible in the interior area as these storms will
have some stronger vertical velocity with them. Even then it will
more than likely be small hail today. The coastal areas will have
much weaker vertical velocity with them, making them more pulse
type storms, making hail much less likely.
The 700mb to 500mb lapse rates will vary from 6.1 c/km along the
coast to around 5.5 c/km in the interior. The mbe velocity looks
to begin weak, but pick up in the afternoon. They generally look
to be from 10kts up to around 20kts in the middle to late afternoon.
This will keep the storms moving today. Making any flooding more
nuisance type than anything else over the metropolitan areas. As for wind
gusts today, looking at the current model sounding, gusts look to be
30 to 40 mph, with dcape is less than 700 j/km. In the interior,
where the dcape is between 800 and 900 j/km, they may be stronger,
with 40 to 50 miles per hour possible.
weak low pressure over the western Atlantic will bring increasing
chances for showers and thunderstorms into the weekend. The wind
will generally be between 5 and 10 kts, keeping seas to around 1
to 2 feet through the weekend.
Preliminary point temps/pops...
West Palm Beach 92 77 94 76 / 40 30 40 40
Fort Lauderdale 91 79 92 78 / 30 30 50 30
Miami 92 78 93 79 / 40 20 50 30
Naples 90 77 91 78 / 30 10 20 10