Scientific Forecaster Discussion
fxus62 kmfl 191144
Area forecast discussion
National Weather Service Miami Florida
744 am EDT Sat Aug 19 2017
generally dry day, though some convection could pass near the East
Coast terminals as the sea breeze develops this morning. Another
round of showers and storms is possible over the interior and near
apf this afternoon and evening. Overnight, an approaching tropical
disturbance will bring increasing convection from east to west
with easterly wind through the period except for the Gulf sea
breeze at apf and gusty variability around convection.
Previous discussion... /issued 405 am EDT Sat Aug 19 2017/
Today through sunday: satellite shows the western Atlantic ridge
has been a little slower to build west, which in turn has slowed
the westward progress of the upper level low across the Florida Straits
and the tropical wave over the Bahamas. The result being the
drier airmass will linger through most of the day across South
Florida as we will remain on the subsident side of the tropical
wave. Convective coverage today should be similar to Friday.
Steering flow will be more southerly than yesterday, as we get on
the back side of the upper level low. This may allow a few more
storms to develop on the west side of the Atlantic Metro early in
the afternoon as the seabreeze gets going. Coverage is still
expected to favor the Gulf Coast with a late day seabreeze
collision, with the threat for strong and gusty storms lingering
due to the drier air and cooler temperatures aloft.
The tropical wave axis looks to cross the area late tonight,
bringing a steady increase in rain chances from east to west by
daybreak Sunday. Best chances look to be along the East Coast in
the morning, then shifting westwards with time as the wave
continues marching west. Tropical airmass with warmer midlevel
temps suggest this activity will be in the form of rain with
embedded storms, with a limited, if any, strong storm threat.
The threat for a few periods of heavy rainfall remain, especially
along the East Coast where the breezy east-southeast flow may
enhance coastal convergence and rainfall amounts. Showers and
storms will then wane from east to west late on Sunday, though
isolated activity may linger into the night.
Monday through wednesday: while there will continue to be run to
run changes in the details for each day, the forecast for the
upcoming week continues to be for a wet and unsettled pattern.
Subsidence and dry air in the wake of the departing upper level low
and tropical wave will make Monday the driest day of the week.
Coverage of afternoon showers and storms will be near, or even a
little below normal. Given the brisk east-southeast flow pattern,
expect scattered showers and storms to move in from the Atlantic and
across the peninsula through the day.
The tropical disturbance located 500 miles east-northeast of the
leeward island (invest 92l) has become less organized in the past 24
hours. The chances for tropical cyclone formation appear to be
decreasing with this system and conditions are only expected to be
marginally favorable for further development. As of 2 am, NHC now
gives this feature a 30%/40% chance of developing into a tropical
cyclone in 2 days and 5 days respectively as it continues moving
west- northwest north of the Greater Antilles and through the
Bahamas early next week. The current forecast have it moving
through South Florida/Cuba tues and Wed.
Models have trended towards a more robust drying on Monday, and a
slower arrival of the deeper tropical moisture on Tuesday along with
lighter winds. This looks to shift the heavy rain threat a little
later in time, more Tuesday night and Wednesday. However we will
need to remain on alert as this setup, tropical moisture with a
modest east- southeast flow, can raise flooding concerns across
the area, especially along the East Coast. All residents and
visitors or South Florida need to continue to monitor this
tropical disturbance through the weekend.
Late next week: upper level trough digging into the eastern US will
weaken the ridge late week, allowing another unseasonable frontal
boundary to move into the state. With flow shifting out of the south-
southwest at all levels, tropical moisture will continue to be
advected across the region toward the boundary, resulting in a
continued rainy pattern that lasts through the week.
Marine...east-southeast winds will prevail for the weekend and
through most of the upcoming week, gradually becoming more
southerly by late next week. Marine concerns over the next few days
will be the increasing winds and storm chances as we see two
tropical waves cross the region.
The first will arrive late tonight into Sunday, with speeds
increasing to 10-15kts overnight, and 15-20kts Sunday night into
Monday, especially over the Atlantic. There won't be too much of a
lull in speeds before the second wave arrives early on Tuesday,
reinforcing the pressure gradient. Speeds look to diminish behind
this wave to 10-15kts for mid to late next week. Seas remain 2ft
or less today, building to 3-4ft on Sunday with occasional 5ft in
the Atlantic on Monday.
Coverage of showers and storms is expected to increase from east to
west later today as the tropical wave approaches. Rain chances over
the open waters will be more scattered on Monday, before increasing
again with the next wave midweek.
There will be an increasing threat of rip currents this weekend
along the East Coast beaches of South Florida, due to the
stronger easterly wind flow.
Climate...Miami tied its record high of 95 on Friday, last set in
Preliminary point temps/pops...
West Palm Beach 93 79 90 82 / 20 50 70 20
Fort Lauderdale 92 80 90 82 / 20 50 60 20
Miami 94 80 91 81 / 20 50 60 20
Naples 93 77 93 77 / 30 20 50 30