Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 261212 AAB

Area Forecast Discussion...UPDATED
National Weather Service Miami FL
812 AM EDT Wed Jul 26 2017



6 PM...

As of 810 AM EDT...Have updated the forecast early this morning
to include all of South Florida under a Heat Advisory, as today
looks to be the hottest day of the year so far. Promoting this
heat is a strong 593+ dam ridge of high pressure at 500 hPa from
the western Atlantic, with the 12z observed KMFL sounding
recording a height of 594 dam. These heights are some of the
highest typically seen for South Florida, and with above normal
low-level temps also expected coupled with sultry dewpoints in the
upper 70s to near 80, the stage is set for a dangerously hot day.

The Heat Advisory is in effect from 11am to 6pm, when the highest
heat index values are expected to occur. During this time, most
areas could see heat index values soar to around 110 degrees, with
a few locations in inland Collier and Miami-Dade counties possibly
reaching or exceeding 113 degrees at times which would meet
Excessive Heat Warning criteria. Earlier this morning, heat index
values will exceed 100 degrees as well, as noted already by
observations along the east coast. Will be monitoring closely the
potential for a short-fused Excessive Heat Warning for portions of
the area based on trends in heat indices later this morning and
into the early afternoon.

Heat safety tips are strongly urged to be followed closely. If
outside, make sure to drink plenty of fluids, stay hydrated, limit
strenuous activity, and take plenty of breaks.

Outside of the heat, a typical summertime day is expected with
chances for showers and thunderstorms initially along the leading
edge of both the Atlantic and Gulf sea breezes, becoming focused
in the interior. Greatest storm coverage today is expected across
the southern interior. The primary threats will be frequent
lightning, locally heavy rain, and brief gusty winds.

In addition to the dangerous heat indices, high temperatures may
make a run at records today, with highs in the low to mid 90s,
with upper 90s possible in the interior.


.PREV DISCUSSION... /issued 730 AM EDT Wed Jul 26 2017/

VFR flying conditions will primarily prevail through the TAF
period ending 12z Thursday. Expect most of the sea breeze activity
later this morning and into the afternoon to remain west of the
east coast sites, with VCTS possible at KAPF beginning at 17z. A
few light showers off the Atlantic may be possible at the east
coast sites early this morning, but should have minimal impacts.
Will continue to monitor storm potential for east coast sites
through the day and amend if needed, with best chances at KMIA and
KTMB. Light and variable winds will become dominated by 10 knot
sea breezes, east/southeast at the east coast sites and westerly
at KAPF by the early afternoon.

PREV DISCUSSION... /issued 357 AM EDT Wed Jul 26 2017/

Today and Tonight: Subtropical ridge gradually weakens today as
a trough across the northern Gulf coast moves southeast. Ridge
will still influence the region with a light east to southeast
flow through the day. Short range models keep this 593dm ridge
over the region with above normal 850mb temperatures for today.
Combination of dewpoints ranging in the low 80s to mid 70s will
lead for another day of heat indices of 100-105F across most of
South Florida with locations over inland Collier and Miami-Dade
County could see heat indices above 108 today. East coast metro
and portion of the interior could see heat index values of above
108 to 110 for an hour during peak heating but return to around
105 for the rest of the afternoon. Therefore, a heat advisory has
been issued for Miami-Dade and Inland Collier starting mid
morning. Overnight lows will be in the mid to upper 70s with some
locations along the east coast in the lower 80s. The blended total
pwats continue around 1.9 to 2 inches over South Florida plus the
latest model sounding show pwats of 2 inches today. The available
moisture in combination with light e to se flow will lead for
both seabreeze to initiate once again this afternoon. Best chance
of showers will be over the waters early in the morning and
transition to interior with sea breeze collision in the afternoon.
The storms that do develop will then propagate and build to the

Thursday and Friday: Another Saharan Airmass is expected to move
through the area. This will reinforce dry mid level airmass in place
across the area lowering the chance of rain Thursday. However, there
is still scattered showers and storms possible in the interior with
sea breezes. High temperatures will remain above normal, with highs
expected to be in the low 90s along the immediate coasts, and mid-
upper 90s for the metro areas and interior South Florida. With
dewpoints in the mid-upper 70s, heat indices both days will climb
back into the 100-108 range. Another heat advisory may be needed
Thursday for at least a portion of South Florida. Subtropical
ridge will continue to weaken towards the end of the week
allowing a more southerly wind flow to return to South Florida.
This southerly flow will bring more tropical moisture into the
region allowing more coverage of showers and storms to increase by
the end of the week into the weekend.

Next week: Upper level shortwave moving across the Great Lakes will
deepen the east coast trough, suppressing the western Atlantic high
to the south and east. Model guidance continue to show the trough
digging as far south as the FL panhandle this weekend, potentially
driving an unseasonably robust surface front by next week. Although
the front may not reach this far south, deeper mid level moisture
ahead of this system and increase in south to southwest flow over
the region will increase the chance of showers and thunderstorms
through the long term period. This southwest flow will limit the
potential for east coast sea breeze to develop.

Ridge extending across the Florida peninsula will keep
southeasterly winds around 10 knots through Thursday, veering
more southerly late week and southwesterly by late this weekend.
Overall speeds will remain light enough for both the Gulf and
Atlantic seabreezes to develop each afternoon, with locally higher
speeds behind the seabreezes.

Afternoon showers and storms will generally remain over the
interior, with more isolated activity over the open waters during
the nights and morning. Coverage of showers and storms expected to
increase as we head into the weekend.

West Palm Beach  94  82  94  81 /  30  10  10  20
Fort Lauderdale  93  83  93  82 /  30  10  10  30
Miami            96  82  93  82 /  30  10  20  30
Naples           94  80  93  79 /  40  30  30  30


FL...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for FLZ063-066>075-168-172>174.


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