Scientific Forecaster Discussion
fxus62 kjax 181922
Area forecast discussion
National Weather Service Jacksonville Florida
issued by National Weather Service Key West Florida
322 PM EDT Fri Oct 18 2019
Short term...(tonight through Monday night)
Wet and windy weather is expected on Saturday due to the
lingering effects of tropical storm Nestor, which is currently
located over the central Gulf and moving quickly northeast toward
the Florida Panhandle. The National Hurricane Center forecasts
the accompanying low to become extratropical soon after moving
onshore, so it will be more characteristic of a strong wintertime
low or gale center as it moves northeast through south-central
Georgia on Saturday afternoon. The low will be gaining a
baroclinic strucutre, complete with a warm front extending to the
east and a cold front trailing back to its southwest. The biggest
impacts will be generally windy weather and a marginal risk of
severe weather on Saturday from one or perhaps two trailing squall
lines and an eventual frontal passage.
At first tonight, southeast winds will increase in the tight
gradient that develops between the landfalling Nestor and a 1020
mb surface high over the mid-Atlantic region. This will be most
pronounced over the Georgia waters, which could have near-gale
southeast winds by sunrise. As you would expect with a low passing
by to the north, winds will become more southerly on Saturday
afternoon, then southwesterly on Saturday evening, and finally
westerly on Sunday morning. The strongest breezes should come on
Saturday PM as the low center makes its closest approach across
south-central Georgia. Wind gusts of 35-45 mph are forecast,
mainly along and north-northwest of a Gainesville to Jacksonville
Beach line. This is where a Wind Advisory is being issued, in
coordination with neighboring offices.
Regarding the severe threat, Storm Prediction Center has a marginal risk drawn for the
entire forecast area in their day 2 outlook valid on Saturday.
Only weak instability of less than 1000 j/kg is expected, but the
kinematics will be favorable for severe weather. It appears that a
warm front will lift northward from Florida into Georgia on
Saturday morning, with a favorable veering low-level wind profile
present in the vicinity of the warm front. Mesoscale models show
at least one and perhaps two separate squall lines, which will
bring the main threat for severe winds and an isolated tornado.
As the low accelerates east-northeast through South Carolina on
Sat night, a cold front will spread eastward through NE Florida/southeast Georgia.
It will be followed by a drier and more stable air mass. Surface
dewpoints will fall into the mid 60s, and full sunshine will
The Post-frontal surface ridge axis will pass east into the
Atlantic on Sunday night, and a stronger cold front will push into
the southern Mississippi Valley on Monday. As a result, low-level
onshore flow off the Atlantic will return on Monday, eventually
becoming southerly on Monday night. Surface-based moisture will
return and deepen, and some warm advection lift will bring a
return of a few showers or some spotty light rain.
Long term...(tuesday through next friday)
A cold front will push through the forecast area on Tuesday,
bringing a chance of rain centered on Monday night and Tuesday. An
even drier air mass and rain-free weather will follow on Wed and
A cold front will settle through the Southern Plains to the
north-central and northwest Gulf next Friday. In advance of this
front, a turn to low-level southeast winds and the development of
a warm advection pattern will support the return of rain chances
to the forecast first to the coast on Thu night, spreading inland
VFR conditions will prevail until around sunset as moisture
increases, lowering ceilings to MVFR through the evening hours.
Sprinkles are expected to occasionally affect kgnv through early
evening, before steady rain overspreads from west to east. MVFR
visibilities and ceilings should prevail this evening into early
morning hours with increasing chance for brief IFR visibilities with
a few heavy rain showers. As potential tropical cyclone 16
approaches the Florida Panhandle overnight, east to southeast winds
will increase to the 10-15 knot range with gusts 20 to 25 knots by
12z Saturday. There is slight chance for thunder late tonight and
Saturday morning, but at this time opted for temporary IFR
visibility heavy rain showers as winds gradually become southeast to
south by midday Saturday.
As the Post-tropical low from tropical storm Nestor tracks quickly
northeast through south-central Georgia on Saturday, near-gale
southeasterlies will develop on Saturday morning, most prominently
along the Georgia coast. As the low passes by to the north, winds
will turn out of the south and peak on Saturday afternoon along
the Georgia coast as a full gale. The low will exit through South
Carolina on Saturday night, leading to decreasing southwest then
Rainfall amounts generally of 1-3 inches are possible through the
early Sunday as the system pushes through the area. The heaviest
amounts are forecast over the Georgia zones and in Florida along
and west of U.S. 301. Due to the progressive nature of the
system, only brief localized flooding potential would be expected
in this situation.
Preliminary point temps/pops...
amg 63 76 62 78 / 90 90 50 10
ssi 70 79 68 79 / 90 90 60 10
jax 69 81 67 83 / 90 100 30 10
sgj 71 81 69 83 / 90 90 30 10
gnv 66 81 67 83 / 90 90 30 10
ocf 68 83 69 85 / 90 90 30 20
Florida...Wind Advisory from 8 am to 11 PM EDT Saturday for coastal Nassau.
Wind Advisory from 8 am to 8 PM EDT Saturday for Baker-Bradford-
Clay-coastal Duval-eastern Alachua-Gilchrist-Hamilton-
inland Duval-inland Nassau-northern Columbia-southern
Georgia...Wind Advisory from 8 am to 11 PM EDT Saturday for Appling-
Atkinson-Bacon-Brantley-coastal Camden-coastal Glynn-Coffee-
inland Camden-inland Glynn-Jeff Davis-northeastern Charlton-
Wind Advisory from 8 am to 8 PM EDT Saturday for Clinch-Echols-
southern Ware-western Charlton.
Am...Gale Warning from 5 am Saturday to 5 am EDT Sunday for waters
from Altamaha Sound Georgia to Fernandina Beach Florida from 20 to 60
nm-waters from Fernandina Beach to St. Augustine Florida from 20
to 60 nm-waters from St. Augustine to Flagler Beach Florida from
20 to 60 nm.
Gale Warning from 5 am to 11 PM EDT Saturday for coastal waters
from Altamaha Sound to Fernandina Beach Florida out 20 nm-
coastal waters from Fernandina Beach to St. Augustine Florida
out 20 nm-coastal waters from St. Augustine to Flagler
Beach Florida out 20 nm.