Hail and Damaging Winds in Florida, June 19, 2020

Area Forecast Discussion
National Weather Service Jacksonville FL
Issued by National Weather Service New Orleans LA
127 PM EDT Fri Jun 19 2020

.AVIATION...
[Through 18Z Saturday]

Cumulus field across most terminals at midday with onshore flow
commencing. SHRA on the seabreeze currently remain south of all
terminals, but soundings would indicate potential for TSRA through
the afternoon hours. For now, will carry VCTS at several
terminals, and handle any anticipated direct impacts with
amendments. Some potential for TSRA development across northern
terminals associated with upper trough rotating through Georgia,
but beginning to look like that may be delayed past max heating.

Once convection dissipates this evening, most terminals should
remain VFR with the possible exception of KVQQ, and will carry
potential for roughly 3SM BR there for several hours before
sunrise.

&&

.PREV DISCUSSION [857 AM EDT]...

.NEAR TERM [Through Tonight]...

A weak surface trough is noted in the guidance today oriented off
the w central FL coast then northeast across our southeast zones
and into the Atlantic. This feature may rotate slightly to the
northwest today and then stall tonight. Another weak trough is
noted across our northern GA zones, which may push slowly
southeast today. Fairly deep moisture is across our southeast
zones, where PWATS of about 1.7 inches are expected. For the
remainder of area, in general the PWATs are about 1.4 inches or
less. A large mid-upper level trough also continues and is located
from the central GOMEX northward into a closed low in western PA.
This trough is forecast to gradually shift offshore of our coast
after midnight.

For early today around sunrise, some showers and storms may be
located well east of the 1st surface trough and near the Gulf
Stream west wall, though a couple of stray showers may move into
our northeast FL coastal zones as a northeast flow north of the
trough brings this weak convection onshore. An east coast sea
breeze will develop today with best chances of showers and storms
along this boundary to the south of JAX and anticipate this
scattered convection to push inland. Other mainly isolated-low end
scattered showers and storms could form over inland southeast GA
with the 2nd trough.

Yesterday, we saw one severe storm that lifted north-northeast
across Marion and Putnam counties, with large hail and damaging
winds. Effective bulk shear value of about 42 kt was noted with
the storm yesterday. For today, shear values may be slightly lower
by about 5-10 kt so we can't rule out an isolated severe storm
late aftn-evening, with hail and damaging wind possible. Highs
today expected to be warmer, with lower 90s more prevalent inland,
but mid/upper 80s along the coast due to the quick development of
the east coast sea breeze.

Tonight...we expect isolated showers and storms through the late
evening hours before dissipating by about midnight-1 am. Lows
tonight near normal mainly in the upper 60s to lower 70s.

.SHORT TERM [Saturday Through Sunday Night]...

A drier air mass will advect eastward and over our region this
weekend as the stubborn closed low over the Mid-Atlantic states
finally gets nudged east-northeastward by a progressive trough
moving across southern Canada and the northern Great Lakes region.
Low level flow will veer to westerly as the base of the closed
trough progresses across the southeastern states, with PWAT values
expected to only be in the 1.3-1.5 inch range during the
afternoon hours. There may be just enough moisture for widely
scattered thunderstorms to develop as the Gulf and Atlantic sea
breeze boundaries collide near the U.S. Highway 301 corridor
during the late afternoon hours on Saturday, with activity perhaps
shifting eastward towards the I-95 corridor towards sunset. One
or two storms may pulse and become strong as mid-level dry air
becomes a factor, with gusty downburst winds and frequent
lightning strikes possible within stronger activity, with storm
motion expected to be east-southeastward only around 10 mph. Less
thunderstorm activity and cloud cover will allow highs to soar to
the low to mid 90s inland and around 90 at coastal locations this
weekend. Maximum heat index values should stay in the 100-105
range as drier air mixes down to the surface and results in
afternoon dewpoint values in the 60s inland.

Low level flow will become west-southwesterly on Sunday as Atlantic
ridging extends its axis westward across south Florida. PWAT
values are progged to fall below 1.5 inches, which should result
in only isolated thunderstorm coverage in between U.S. Highway
301 and I-95 during the late afternoon hours, which is about where
the Gulf and Atlantic sea breezes will collide. Lows this weekend
will fall to the upper 60s inland to the low and mid 70s at
coastal locations.

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

The dry and subsident air mass will begin to erode by Monday
afternoon as southwesterly low and mid level flow gradually
strengthens downstream of an upstream trough that will be
digging southeastward through the Ohio and Tennessee Valleys.
Widely scattered convection may develop late on Monday afternoon
and through the early evening hours across the southern portions
of the St. Johns River basin, where deeper moisture will reside
and sea breezes are expected to collide, with only isolated
coverage elsewhere. Highs on Monday and Tuesday will climb to the
mid 90s inland and around 90 at the Atlantic coast, with afternoon
heat index values of 100-105.

Diurnal convective coverage will then gradually increase, with
widely scattered afternoon and evening convection on Tuesday
and then scattered to numerous coverage for Wednesday and Thursday
afternoons. Activity could linger well into the evening hours
beginning around midweek as temperatures aloft begin to cool off
and deeper moisture overspreads our area from west to east.
Thunderstorms along the I-95 corridor will likely pulse and become
strong as activity intersects a pinned Atlantic sea breeze
boundary. Prevailing west-southwest low and mid level flow will
result in continued hot temperatures before afternoon convection
develops, with low to mid 90s expected region-wide on Wednesday
and Thursday. Increasing humidity levels will drive heat index
values up towards 105 degrees by midweek. Lows next week will
remain in the 70s.

.MARINE...

A weak sfc trough will be over the marine area today through
Saturday morning, allowing for some isolated to scattered showers
and storms at times, with best coverage over the southeast
portion, with generally lower chances of showers and storms
Saturday through at least Monday as sfc ridge is anticipated to
build a little strong over the central FL portions. Winds will be
at most 10-15 kt over the next few days and seas generally around
2-4 ft. The ridge will drop a little southward Tuesday as a weak
front moves into the ern U.S. and this could result in a few more
storms over the coastal waters.

.FIRE WEATHER...

Hot temperatures and less thunderstorm coverage this weekend
will result in minimum relative humidity values falling to
near 35 percent at all inland locations on Saturday and
Sunday. Light westerly transport winds are forecast on
Saturday, with gradually strengthening southwesterly transport
winds forecast on Sunday, resulting in good dispersion values
for inland locations. The Atlantic and Gulf coast sea breezes
will move well inland both days, resulting in onshore winds
sustained at 10-15 mph at coastal locations during the
afternoon hours.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  69  92  70  94  70 /  20  30  10  20  20
SSI  73  87  74  90  75 /  10  20  10  10  10
JAX  70  92  70  93  71 /  10  40  10  20  20
SGJ  71  90  72  92  74 /  10  30  10  10  20
GNV  69  93  69  93  70 /  30  30  10  20  20
OCF  70  92  69  92  71 /  30  20  10  20  20

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&

Special Weather Statement
National Weather Service Jacksonville FL
Issued by National Weather Service New Orleans LA
300 PM EDT Fri Jun 19 2020

FLZ025-032-033-125-133-192000-
Coastal St. Johns FL-Inland Duval FL-Clay FL-Coastal Duval FL-
Inland St. Johns FL-
300 PM EDT Fri Jun 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN ST. JOHNS...NORTHEASTERN
CLAY AND SOUTHEASTERN DUVAL COUNTIES UNTIL 400 PM EDT...

* At 300 PM EDT, National Weather Service meteorologists were
  tracking a strong thunderstorm near Fruit Cove. This storm was
  nearly stationary.

* Nickel size hail and winds in excess of 45 mph possible with this
  storm.

* Locations impacted include...
  Fruit Cove, Mandarin, World Golf Village, Fleming Island, Nocatee,
  South Ponte Vedra, Bayard, Durbin, Switzerland and Guana River
  State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These winds can down small tree limbs and branches, and blow around
unsecured small objects. Seek shelter in a safe building until the
storm passes.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm. If
you can hear thunder, you are close enough to be struck! Seek a safe
shelter inside a building or vehicle.

To report severe weather, contact your nearest law enforcement
agency. You can also share your report with NWS Jacksonville on
Facebook and Twitter.

&&

LAT...LON 2992 8161 3010 8173 3026 8146 3002 8132
TIME...MOT...LOC 1900Z 242DEG 4KT 3007 8155

KLG