Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Miami Florida
755 PM EDT Monday Jul 27 2015
Tranquil night to follow. Updated grids for current trends. Weak
low pressure continues to drift north through the eastern Gulf of
Mexico/West Coast of Florida. Still may generate some showers along
the West Coast tonight.
Previous discussion... /issued 719 PM EDT Monday Jul 27 2015/
overall pattern shifting to a more typical Summer/wet season
one...as low pressure and surface boundary weaken and retreat
normal. Southwest wind will continue...averaging 10 knots or less.
Shower chances return Tuesday afternoon...with earlier initiation
at kapf. However...probs are low thus thunderstorms in the vicinity not introduced at this time.
Thunderstorm chances around 20 percent at Miami-Dade terminals...so elected to
leave those dry with 0z taf issuance.
Previous discussion... /issued 445 PM EDT Monday Jul 27 2015/
As this past weekend's eastern Gulf low pressure continued to
slightly weaken and drift north, drier midlevel air has filled The
Gap covering the southeastern third of the region. Showers and
storms today have been less numerous, although just a few remain possible
through the early evening. Meager 500 mb temperatures and unimpressive lapse
rates have also kept coverage down. The wind profile however is
still reminiscent of a fall or winter one, thus any smaller
isolated showers/storms could easily produce a 45 miles per hour wind gust.
Although subtle low pressure remains nearby North Florida much of
this week, with southwest flow over our region, enough relatively
drier air will remain in the midlevels to keep probability of precipitation mostly below
50 percent for much of the week. Probability of precipitation from local blends actually
may be too optimistic considering precipitable waters and moisture depth are
still favorable for at least scattered convection, with any added
nudge from colliding outflow boundaries/sea breeze sufficient to
punch through the dry layer. At least until middle to late week, 500 mb
temperatures and midlevel lapse rates remain unimpressive, so likely a
combination of these factors is producing such dry quantitative precipitation forecast forecasts
from the model suite. Conds a little more favorable across the
lake region and Palm Beach County, so that is where the highest
probability of precipitation will reside. The GFS even features a decent midlevel shortwv
dropping south by Wednesday and Thursday over the lake region but still
keeps quantitative precipitation forecast rather dry. Not totally buying a dry solution so probability of precipitation
were adjusted upward a bit from local blends Wednesday and Thursday,
especially with southwesterly winds not strong enough to prevent
an East Coast sea breeze from forming. In addition, with only slt
chance to chance probability of precipitation forecast and southwest flow, maximum T will likely
come in a few degrees warmer than local blends at East Coast sites
especially on Wednesday so some adjustments were made there too.
Both the European model (ecmwf)/GFS continue to show a weak upper low approaching
South Florida late this week and this weekend, potentially moving
across the Bahamas and Florida Straits per the GFS but taking a
more northerly track per the European model (ecmwf). This will change the current
regime in several ways. Additional moisture will arrive, 500 mb temperatures
and midlevel lapse rates will become more favorable as it
approaches, and surface flow will back to the south and even the
southeast. Regardless of model solution, this slight weakness in
the 500 mb ridge should lead to more numerous storms, especially
across the interior and also East Coast metropolitan areas this weekend.
Weak low pressure will meander from the northeastern Gulf to the
Panhandle of Florida through the week. However, a constant supply
of relatively drier air in the midlevels will keep storms from
becoming too numerous. Southwest winds are expected through much
of the week but will become lighter and from the south to
southeast by the weekend. A few stronger storms are possible over
the Atlantic waters this afternoon and evening.
Preliminary point temps/pops...
West Palm Beach 79 94 78 91 / 20 40 30 40
Fort Lauderdale 80 93 79 92 / 20 30 20 30
Miami 79 94 79 93 / 20 20 10 20
Naples 79 90 79 90 / 20 30 20 30