Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Miami Florida
1013 PM EDT Thursday Sep 18 2014
Deep moisture and subtle convergence overnight will keep some showers
in the forecast even for the southern peninsula, including the
Gulf and Atlantic waters. Trough remains near Lake Okeechobee.
Precipitable water from 0z sounding was 2.16".
Previous discussion... /issued 803 PM EDT Thursday Sep 18 2014/
Line of slow moving showers and storms may train over fll, with
brief IFR possible over the next few hours. Otherwise, most storms
have dissipated with only scattered showers through the night.
Somewhat better chance of this occurring at kapf so used vcsh for
the second part of the night. A stronger upper level disturbance
will combine with the weak boundary just to our north to produce
more widespread storms on Friday, if clouds left over from tonight
do not stunt convection. Since probability of precipitation are high and tomorrow
afternoon is outside of 9 hrs, used probability 30 groups in the tafs.
Previous discussion... /issued 333 PM EDT Thursday Sep 18 2014/
Discussion...satellite imagery shows a band of cloudiness
extending from the western Atlantic between the Carolinas and
Bermuda...extending southwest to across the northern Bahamas, the
southern tip of Florida and into the Gulf of Mexico. This is
associated with an old frontal boundary/trough. Both the
operational 18.12z GFS and European model (ecmwf) are in agreement in showing low
pressure developing along this boundary as a shortwave digs down
across Georgia tomorrow.
Both models place this low development just north of the Bahamas
Friday night-Sat...with movement then to the northeast as the trough
grabs this low and sends it away from our area. In the meantime,
deep moisture will be present across South Florida over the next few
days. Moisture profiles/forecast soundings show high moisture in
the middle to upper levels, but there is some drier air in the lower
levels. This set up is classic cloudiness but more limited
thunderstorm activity. So the forecast reflects this with only a
slight chance of thunderstorms through Saturday. However, maintained
high probability of precipitation as there will be quite a bit of shower activity.
Precipitable waters look to average in the 2-2.15 inch range. With these high
moisture levels and low pressure developing just off to our
northeast, convergence southwest of this low will need to be
monitored for the threat of training/locally heavy rain. However,
right now am thinking this threat is low as cloudiness will limit
heating/instability and convective potential. /Gregoria
Saturday night through Wednesday...
convective activity will become more diurnal this weekend as the
developing low exits to the northeast Saturday night. By Sunday,
the trough over the eastern US weakens and pulls back to the
north, allowing high pressure to slowly build back in over the
Gulf. With a lighter flow over South Florida, the convection will
once again become diurnal, with the main trigger, the sea breezes.
The interior areas look to be the most favorable for development
each day, although either coast could also see showers and
thunderstorms each day through the middle of next week. /Si
Marine...light wind flow will prevail into early next week as the
pressure pattern remains weak. Any increasing winds with the
potential low development north of the Bahamas are forecast to
remain northeast of the South Florida local marine area. Seas will
remain below 4 feet.
Preliminary point temps/pops...
West Palm Beach 76 85 74 84 / 10 70 30 60
Fort Lauderdale 77 86 75 85 / 40 70 40 60
Miami 76 86 74 86 / 40 70 30 60
Naples 76 86 74 83 / 20 70 40 60