FXUS62 KJAX 251938
Area Forecast Discussion
National Weather Service Jacksonville FL
338 PM EDT Fri May 25 2018
...HIGH RAIN CHANCES SUNDAY AND MONDAY...
...LOCALLY HEAVY, FLOODING RAINFALL POTENTIAL...
.Near Term...through Saturday...
As the East coast sea breeze pushes further inland this afternoon,
convection is expected to focus along and West of a Waycross to
Gainesville line. A boundary extending South through SE GA, from a
weak low to the North, will couple with the sea breeze interactions
and diurnal heating to keep the convection going this afternoon.
The convection will dissipate this evening with the loss of diurnal
heating, and the remaining convection may drift East as the East
coast sea breeze weakens. Any storms which develop this afternoon
will be slow moving due to light flow, resulting in locally heavy
rain. Areal coverage of convection will be lower on Saturday, as
drier air advects into Eastern counties as East coast sea breeze
pushes well inland. The best potential for convection Saturday will
be over Western counties.
Above seasonal temperatures will be expected Tonight, with near
normal on Saturday.
.SHORT TERM...Sat Night through Mon Night...
Synopsis...High rain chances with muggy, humid conditions.
Locally heavy, flooding rainfall possible.
Plume of deep tropical moisture will over overspread the FL
peninsula Sat night with precipitable water content rising to
2-2.5 inches as Sub-Tropical Storm Alberto drifts northward across
the central Gulf of Mexico. A broad, more persistent rain shield
is expected to sweep south to north across the forecast area early
Sunday, with coastal convergence in the morning under stronger
ESE flow focusing the higher rainfall amounts along the local
coast and Altamaha River basin within an outer rainband as it
drifts north and inland. Sunday afternoon and evening, a heavier,
more widespread rainfall band is expected to stream across much of
the FL peninsula and across SE GA. Although widespread, and
potentially localized flooding rainfall is expected Sunday,
especially for inland areas that have received 3-6 inches of
rainfall within the past week, do not expect a lot of tstorm
coverage due to limited surface based instability, but convergence
near the coast and within rainbands could certainly support a few
rotating cells as low level 1km helicity nears 100-150 k2/s2. Sun
night Alberto is expected to near the central Gulf Coast region,
with most forecast model guidance indicating the center between
Apalachee Bay and New Orleans. Official NHC forecast guidance
advertised a 1 in 10 chance of sustained tropical storm force
winds (39 mph or more) along and west of a Homerville to Ocala
line Sunday evening into Sunday night with decreasing probability
into Monday, thus probability of any portion of the local forecast
area experiencing tropical storm force winds from Alberto is very
low at this time. Rainfall is expected to generally fade over
land after 06Z Mon as low level flow veer more southerly, while a
more robust ongoing band of rainfall will likely position just
offshore of the first coast.
After sunrise Monday, moist, southerly flow will continue with
high precipitable water content draped overhead as Alberto slowly
nears the mainland of the Gulf Coast region. Locally, rainfall
will increase along both the Atlantic and Gulf coasts aided by sea
breezes as there will be some drier mid level air pivoting
overhead which could bring some peeks of sunshine. With high
PWATs, streaming unidirectional south winds, and the potential for
sea breeze development with more surface based instability,
Monday convection certainly will have the potential to once again
produce locally flooding rainfall rates, with training cells more
probable drifting S to N within diurnally enhanced convergent
bands. Also appears to be a a greater potential for a few strong
to severe storms capable of wet downbursts due to precipitation
loading as updraft development will be better enhanced with
surface heating. Once again a gradual fade in rainfall is expected
Monday night inland.
Official rainfall guidance from the Weather Prediction Center
(WPC) during this time frame is generally an additional 2-4
inches, with locally higher amounts.
The airmass will feel thick, heavy, humid and generally uncomfortable.
Temperatures will trend below normal for highs due to cloud cover
with values in the low/mid 80s. Low temperatures will range
generally in the upper 60s inland Sat night to the lower 70s Sun
night with the increased moisture. For Memorial Day, heat index
values will near the mid 90s due to such high moisture content.
.LONG TERM...Tue through Fri...
Unsettled weather will continue this period with elevated rain
chances each day due to lingering tropical moisture over the area
as the Sub-Tropical Storm Alberto drifts NNE across the southeast
region. Convection will be diurnally enhanced with sea breezes Tue
with a focus for best rain chances across the interior in the
afternoon and evening with locally heavy rainfall the main concern
with PWATs still 2-2.4 inches. Steering flow transitions Wed to
SW with lingering high moisture as the circulation that was
Alberto begins to drift north of the region. SW steering flow
continues over the local area Thu, but with drier air as PWATs
fall to 1.5-1.8 inches favoring slightly lower rain chances with a
stronger prevailing west coast sea breeze regime not supporting
the east coast sea breeze to make much inland push. By Fri, a
drier WNW steering flow develops as the mid level trough axis
trailing from the Alberto circulation pushes across the area. Once
again, will continue with elevated rain chances with lingering
moisture and some passing weak forcing associated with the passing
mid level trough.
High temperatures will trend near to slightly below climo with
elevated rain chances each day next week with highs in the
mid/upper 80s. Low temperatures will trend above normal with
values in the lower 70s.
Convection is expected to develop and move further inland this
afternoon, mainly affecting KGNV, but restrictions can not be ruled
out at other area TAF sites. Convection should dissipate by
midnight, with the best chance for convection on Saturday inland.
High pressure will be East of area waters through early next week.
Tropical storm Alberto is forecast to move North through the central
gulf this weekend into early next week. As a result of the tropical
system, winds and seas will increase over the weekend, especially so
Rip Currents: Moderate risk through Saturday. Elevated risk will
continue through the holiday weekend.
.PRELIMINARY POINT TEMPS/POPS...
AMG 69 87 69 80 / 70 20 20 80
SSI 74 81 74 79 / 40 10 40 80
JAX 72 86 71 83 / 40 10 50 80
SGJ 73 83 71 81 / 30 10 60 80
GNV 70 86 70 81 / 60 40 40 80
OCF 70 84 69 82 / 60 40 40 80
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