FXUS62 KJAX 060046

Area Forecast Discussion
National Weather Service Jacksonville FL
846 PM EDT Fri Jun 5 2020


Warm, humid conditions continue this evening with 8 PM
temperatures across the area still in the low 80s to upper 70s and
dewpoint temperatures in the 70s. Light rain will remain possible
overnight, mostly across north-central Florida. No major changes
wit this forecast update.



.NEAR TERM [Through Saturday]...

The cirrostratus shield will continue to advance northward and
will blanket all of inland southeast Georgia late this afternoon,
which may put a lid on convective coverage where hotter
temperatures were experienced today, although some isolated
convection may be possible early this evening along the Altamaha
River as outflow boundaries from convection over central Georgia
press southward into a moderately unstable air mass. Otherwise,
the shield of heavy showers associated with a deep surge of
tropical moisture associated with Tropical Storm Cristobal will
cross I-4 before sunset, with short-term, high resolution guidance
indicating that this shield will erode after sunset as mostly
stratiform rainfall reaches north central Florida. A lull in
rainfall is likely overnight, followed by another round of
stratiform rainfall overspreading the Nature Coast and Florida
Big Bend region during the predawn hours as Cristobal begins to
strengthen over the southern Gulf of Mexico. This rainfall should
reach into north central Florida and southern portions of the
Suwannee Valley by sunrise. Otherwise, cirrostratus will continue
to thicken over the rest of our region, keeping lows mostly in the
lower 70s.

Troughing aloft over the Tennessee and lower Mississippi Valleys
and stout ridging building over the eastern Bahamas and Cuba will
keep deep southwesterly flow in place over Cristobal and over our
region this weekend, which will focus several convective bands
over the eastern Gulf of Mexico and the Florida peninsula through
Sunday morning. Guidance indicates that a particularly heavy outer
band will rotate north-northeastward from the Florida peninsula on
Saturday afternoon, with heavy downpours progressing into north
central Florida by early afternoon and then the rest of northeast
Florida by the mid to late afternoon hours. PWATS will rise to the
2.2-2.4 inch range by sunset, increasing the potential for heavy
rainfall amounts during a relatively short period of time within
this initial outer rain band that will move through our region.
Overall soil moisture levels remain too low for a Flood Watch in
north central Florida and the Suwannee Valley at this time, but
localized flooding will be possible in these locations,
particularly in urban and low lying areas, given warm
temperatures aloft and the deep tropical air mass that will be in
place. Highs on Saturday will again be warmer in southeast
Georgia, where mid 80s will prevail, while afternoon rainfall
keeps highs closer to 80 in north central Florida.

.SHORT TERM [Saturday Night through Monday Night]...

Tropical Storm Cristobal will continue moving northward through
the central and then the northern Gulf of Mexico on Saturday night
and Sunday. Global models indicate that significantly drier air
currently positioned west and northwest of Cristobal will wrap
around the tropical cyclone's circulation by early Sunday, which
should begin to shutoff convective potential over our region
towards noon on Sunday. Bands of heavy showers and a few embedded
thunderstorms will continue to stream northward through our area
on Saturday night, with some model guidance even depicting locally
heavy rainfall shifting over southeast Georgia overnight,
providing more beneficial rainfall for those locations through
Sunday morning. Heavy rainfall and localized flooding will
continue to be our main hazards locally, with a few training bands
of convection possible in the Suwannee Valley and north central
Florida, where higher rainfall amounts of 3-4" will occur on a
widespread basis this weekend, with locally higher totals
possible. Rainfall amounts elsewhere in northeast Florida of 1-3"
are forecast this weekend, while later arrival of downpours
keeping totals in southeast Georgia mostly below 1 inch.

The dry slot advecting into our region on Sunday afternoon should
result in breaks in the thick cloud canopy, allowing highs to
climb to the mid and possibly upper 80s inland, while breezy
southeasterly winds keep coastal highs mostly in the lower 80s.
Convective coverage may increase somewhat by late Sunday afternoon
and early evening along inland moving sea breeze boundaries as
instability increases, with most of Cristobal's outer bands
shifting west of our region as the cyclone reaches the Louisiana
coast. Deep-layered ridging will continue to shift westward and
directly over our region by Monday afternoon, with morning
subsidence allowing for more insolation that should drive highs
back into the lower 90s inland, with active afternoon sea breezes
keeping coastal highs in the mid 80s. Scattered to numerous
thunderstorms should congregate along U.S. Highway 301 by late
afternoon Monday as the Gulf and Atlantic sea breezes collide,
with a few storms pulsing to strong levels as greater instability
develops locally, with downburst winds and heavy rainfall being
the primary hazards. Convection should remain mostly diurnal in
nature early next week, and a tropical air mass will result in
lows around 70 degrees.

.LONG TERM [Tuesday Through Thursday Night]...

Deep-layered ridging in place locally on Tuesday will begin to
break down by midweek as ridging aloft builds over Texas and
forces Cristobal's remnant tail of deep moisture slowly eastward
across the Florida panhandle. Relatively light flow throughout
the atmospheric column on Tuesday should allow for widespread
diurnal convection to erupt along inland moving sea breeze
boundaries. Stronger surface ridging should then build north of
our region towards midweek, possibly advecting a drier and more
subsident air mass into our area from the Atlantic waters by
midweek, trapping Cristobal's remnant moisture just west of our
area. This moisture may then reach our region late in the week.
Higher convective coverage on Tuesday may keep highs in the upper
80s to near 90 inland, and then deeper easterly low level flow
should keep highs mostly in the mid to upper 80s for most
locations on Wednesday and Thursday. Lows may fall into the mid
to upper 60s at inland locations by midweek as a drier and more
subsident air mass potentially moves overhead, with onshore flow
keeping coastal lows in the lower 70s.

[Through 00Z Sunday]

Patches of light rain this evening, mostly across north-central FL
and the NE FL coastline. Increasing chances of showers after 06z
near GNV, after 16Z everywhere else. Winds mostly from the
southwest this evening, becoming light and variable in the next
couple of hours. Winds will pick back up late Sat morning/early
Sat afternoon, becoming southerly at 5-10 kt, with southeast winds
at GNV.


Tropical Storm Cristobal will emerge over the southern Gulf of
Mexico early this evening and will be steered northward towards
the central Gulf coast region this weekend by Atlantic ridging
that will be centered just east of the Bahamas. Prevailing south-
southwesterly winds tonight will shift to south-southeasterly by
Saturday afternoon, with Caution speeds of 15-20 knots expected
throughout our local waters through Saturday evening. Seas should
build to 3-5 feet offshore by Sunday, with 2-4 foot seas expected
this weekend near shore. Winds and seas will then diminish early
next week as Cristobal's remnants move into the lower Mississippi


Southwesterly surface and transport winds this afternoon and
evening will shift to southerly overnight. Heavy showers and
embedded thunderstorms will then overspread north central Florida
by the early afternoon hours on Saturday and will reach the rest
of northeast Florida by the late afternoon and early evening
hours. Surface and transport winds will shift to east-
southeasterly in northeast and north central Florida, with
cloudiness and widespread rainfall resulting in low daytime
dispersion values. Showers and thunderstorms will increase in
coverage across southeast Georgia from Saturday evening through
Sunday morning. Surface and transport winds will remain southerly
on Saturday and Saturday night in southeast Georgia. Higher
rainfall coverage will then shift to the Suwannee Valley and
inland portions of southeast Georgia by Sunday afternoon, with low
daytime dispersion values expected for most locations.


Heaviest rainfall amounts this weekend are forecast to occur in
north central Florida and the Suwannee Valley, where widespread
3-4 inch totals are expected, with locally higher totals possible.
Widespread 1-3 inch totals are forecast elsewhere across northeast
Florida, with totals likely an inch or less throughout most of
southeast Georgia. Given antecedent dry soil moisture, our main
concerns for localized flooding this weekend will be in urban and
low-lying locations, but locations in the Suwannee Valley and
north central Florida will be closely monitored on Saturday night
and Sunday for training bands of convection on the far eastern
periphery of Cristobal's circulation.



AMG 71 86 70 86 71 / 10 40 40 50 20
SSI 74 83 74 83 75 / 20 40 50 50 20
JAX 71 82 72 85 72 / 20 80 80 60 20
SGJ 72 80 73 83 74 / 20 80 80 60 30
GNV 71 80 71 84 72 / 30 90 90 70 30
OCF 71 80 72 84 72 / 40 90 90 70 30


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