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Area Forecast Discussion (AFD)

Issued by Tampa Bay Area, FL (TBW)

FXUS62 KTBW 211915

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
315 PM EDT Mon May 21 2018

.SHORT TERM (Tonight-Tuesday)...
Mid/upper level disturbance over the Florida Panhandle will drift
slowly north into Alabama through Tuesday with the plume of deep 
tropical moisture continuing to be pulled north across the Florida 
peninsula. The scattered to numerous showers and thunderstorms 
this afternoon will wind down this evening becoming isolated
overnight across our area with majority of the convection over 
the eastern half of the Florida peninsula. For Tuesday we'll see
another day of scattered to numerous showers and storms starting
in the late morning/midday hours and continuing into the evening.
Locally heavy rainfall with flooding of low lying and poor 
drainage areas will remain the biggest concern. Temperatures will
remain near normal with overnight lows in the upper 60s to lower
70s and daytime highs in the lower to middle 80s on Tuesday. 

.MID TERM/LONG TERM...(Tuesday Night through next Monday)...
The main concerns through the longer term forecast period will be 
a stubborn pattern favoring locally heavy rainfall, and low-lying,
riverine flooding concerns to go along with it.

The eastern Gulf of Mexico and Florida peninsula will continue to 
reside underneath a broad cyclonic flow pattern during the middle 
of the week. At least for Wednesday and Thursday there are 
indications that the amount of deep moisture over the region will 
decrease, and hopefully give a break to the widespread rainfall 
coverage for a couple days. This is not to say the forecast is 
dry, but with no significant upper support for ascent and less 
available moisture / lower PWs, we can expect a more typical 
distribution of diurnal storms across the area. These can locally 
drop some heavy rainfall, but the potential for widespread 
rainfall, which works to impact rivers to a greater degree, will 
have decreased...briefly. 

The next significant concern for the heavy rain threat comes from
a disturbance lifting out of the NW Caribbean later Friday into 
Saturday. This system is very disorganized currently, and this 
makes confidence in its exact evolution lower. The National 
Hurricane Center gives this system a 20% chance of tropical 
development through the next 5 days, and this is about all one can
do given the state of the current system. In general, the 
tropical development potential is not the real concern with this 
system, as the impacts to our area will mainly be heavy rainfall /
flooding either way. We need to be focusing on the rain threat at
this point. The track and organization of this system will 
obviously be big players in the rainfall threat equation. However,
there is good agreement that this system will move somewhere 
between the FL west coast and the central Gulf of Mexico. 
Essentially any solution in this range puts us within the deep 
southerly moisture and heavy rainfall threat area. If trends went 
further west, then the FL peninsula may end up outside the main 
moisture plume, but currently an ensemble forecast solution does 
not support this scenario.

Unfortunately, this would suggest another weekend with not much
sun, and a lot of clouds / rain. Soils are getting very saturated
at this point and rivers are running high (some already in flood 
stage). Additional heavy rainfall is not welcome scenario for many
spots, and hence we will continue to closely monitor the evolution 
of this disturbance for next weekend.

Temperatures should run near or just below normal for Wednesday
and Thursday, and then run below normal for Friday and the weekend 
due to the potential for abundant clouds and frequent showers.


Scattered to numerous showers and a few thunderstorms will
continue into early this evening producing MVFR/local IFR 
conditions along with gusty winds up to around 30 knots. After 
22/00z the showers and storms should wind down with mainly VFR 
conditions prevailing overnight into early Tuesday morning. More
convection expected to develop around midday Tuesday.


Southeast flow will continue at 15 knots or less for the next few 
days with the west coast sea breeze trying to develop Tuesday and 
Wednesday afternoons. Winds and seas will remain below advisory 
levels through the period with the main hazard continuing to be 
the showers and thunderstorms with some of the stronger storms 
capable of producing strong gusty winds and locally rough seas.


No fire weather hazards are expected for the next several days as
relative humidity values are expected to remain well above
critical levels. 


.Preliminary Point Temps/PoPs...
TPA  72  86  72  86 /  30  70  30  50 
FMY  71  86  72  86 /  40  60  20  60 
GIF  71  86  70  87 /  30  70  20  50 
SRQ  71  85  71  85 /  40  60  30  50 
BKV  69  86  69  88 /  30  70  20  50 
SPG  74  86  73  86 /  40  60  30  50 


Gulf waters...None.