Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/14/20
Area Forecast Discussion
National Weather Service Mobile AL
1037 PM CDT Sun Sep 13 2020
.NEAR TERM /Now Through Monday night/...A well defined upper level
anticyclone is now atop Tropical storm Sally and this along with
lessening shear has caused deep convection to become better
organized at the center of Sally`s low level circulation over the
northeast Gulf. In fact, aircraft recon indicates that the center
has reformed within the deep convection to the northeast of the
previous center advisory location which has resulted in an
eastward shift to the track forecast. Sally is forecast to
intensify to a hurricane Monday as it tracks west northwest over
very warm SST`s over the northern Gulf and a continued favorable
upper air pattern. Sally is expected to be approaching the MS
Sound Monday evening and be roughly 80 miles south of the MS coast
just east of the southeast tip of Louisiana.
Late in the afternoon, forecasters saw the development of the
first well defined outer spiral band from Sally along and north of
I-10. Individual storm clusters within the band were very
efficient in mixing down higher momentum air/brief strong wind
gusts as well as bursts of heavy rain. Radar data shows this band
has weakened. Another band is rotating westward across the open
Gulf waters. We are now in an environment where we can expect to
see rain bands develop and perhaps quickly as Sally gains more
latitude. Brief strong wind gusts to tropical storm force (40-50
mph) and locally heavy rain can occur in the more well defined
bands. /10
Given the re-formation of the center and the eastward shift in the
track has resulted in an increased threat level of local impacts
to the area. It is important to stay vigilant and have an action
plan in place as short term adjustments can still occur. Latest
updates to the watch/warning/advisory section are listed below. Please
make sure to continue to check our webpage (weather.gov/mob) as
well as the National Hurricane Center (www.hurricanes.gov) for the
latest updates and information on Sally.
&&
.PREV DISCUSSION... /issued 703 PM CDT Sun Sep 13 2020/
AVIATION...
00Z issuance...We are now in the beginning stages of Sally`s rain
bands. The first organized band, displaced to the north of Sally,
has developed over the past few hours along the I-10 corridor.
Shra/Tsra within the band will track west southwest around 30 MPH
and will be efficient in producing brief strong wind gusts, brief
brief reductions to vsby with passage of +RA and lowering cigs.
/10
PREV DISCUSSION... /issued 443 PM CDT Sun Sep 13 2020/
NEAR TERM UPDATE /Now Through Monday/...Aloft, a ridge will
continue to build over the western CONUS, with a northern stream
trough over the Great Lakes and upper Ohio Valley. A surface cold
front, draped all the way from the upper Ohio Valley down through
the ARKLATEX and over central Texas, will continue its southeastern
progression through Monday. Meanwhile, Tropical Storm Sally (TS
Sally) continues its slow west-northwest trajectory over the eastern
Gulf of Mexico. At this time, TS Sally is forecast to strengthen
into a hurricane by early Monday afternoon and make landfall over
the far southeastern portion of Louisiana late Monday night into
early Tuesday morning. However, there still remains uncertainty in
the track and intensity of this storm. It is important to stay
vigilant and have an action plan in place, as the track and
intensity forecasts for TS Sally (and associated impacts to the
local area) could continue to change as the system evolves.
Therefore, please make sure to continue to check our page as well as
the National Hurricane Center (www.hurricanes.gov) for the latest
updates and information.
For sensible weather through Monday, expect an increase in rain
chances with the influx of tropical moisture. PWATs will increase
from 1.8-2.2 inches today to 2.3-2.5 inches by Monday afternoon with
the approach of TS Sally. Model MLCAPE values are also between 500-
1000 J/kg area-wide during this time. Isolated to scattered showers
have been the story today, particularly near the coast. This will
then increase to in coverage by tomorrow afternoon. In addition,
gusty winds are expected with rain bands that move northward over
the area from Sally. At this time, tropical storm force wind gusts
(40-50 mph) are possible for portions of southeast Mississippi and
coastal Alabama, whereas occasional wind gusts (40-50 mph) are
possible further inland and mainly along the coast of the western
Florida Panhandle. Frequent tropical storm force wind gusts are
anticipated along the immediate coast. Although there is the
potential for tornadoes along the immediate coast (Alabama and
Florida), southeast Mississippi, southwest Alabama, and portions of
the western Florida Panhandle (as is typical with tropical systems),
flooding and storm surge are the major threats with this particular
system. With this storm being very slow-moving, this could
potentially be a prolonged event with locally heavy rainfall and the
potential for flash flooding. At this time, storm total rainfall is
forecast to range between 8-16 inches (with locally higher amounts
up to 24 inches) for coastal Alabama, southeast Mississippi, and the
far western Florida Panhandle. In addition, storm surge between 2-4
feet is predicted along the coast of Alabama as well as Mobile Bay,
with 1-3 feet further east along the Florida coast. However, the
aforementioned totals for rain and surge are dependent on the track
of TS Sally and could increase should it shift further east. Thus,
it is important to continue to check back for updates as short fused
changes to the forecast track and intensity are possible. Further
impacts to the local area include a HIGH RISK of rip currents as
well as dangerous high surf (large breaking waves of 8-12 feet)
through at least midweek.
A Hurricane Watch and a Tropical Storm Warning remains in effect for
portions of coastal Alabama and a Tropical Storm Warning is also in
effect along the coast for the northwest Florida panhandle counties.
Additionally, a Tropical Storm Watch was issued this afternoon for
portions of southeast Mississippi. The Flash Flood Watch continues
for southwest Alabama, southeast Mississippi, and the western
Florida panhandle as well. Along the coast, a Storm Surge Watch
remains in effect for the Alabama coast (including Mobile Bay) and a
Coastal Flood Advisory is in effect for the western Florida
panhandle (including bays). Lastly, a High Surf Warning continues
along the Gulf beaches of the Alabama and western Florida panhandle
coasts. /26
SHORT TERM /Monday night Through Wednesday night/...Sally is
expected to make landfall as a hurricane Monday night across
portions of southeast Louisiana. The center is expected move north
into south central Mississippi by Wednesday morning then turn
northeast during the day on Wednesday. The threat for heavy
rainfall, gusty winds and tornadoes will be greatest across
portions of our forecast during the short term period. Tropical
storm force wind gusts could be possible along portions of the
coast as the storm makes its closest approach Monday night into
Tuesday. Peak flash flooding potential will be during this time as
well. Dangerously high surf, life threatening Rip currents will
also possible during this period. Coastal flooding potential due
to storm surge will be greatest Monday night Tuesday, although
specific impacts for this will be dependent on the exact track and
intensity of Sally. Please see the latest forecast from the
National Hurricane Center for updates on Tropical Storm Sally. /13
EXTENDED TERM /Thursday Through Sunday/...Sally is expected to
weaken to a depression as it moves into north Alabama on Thursday.
This slow movement along with the curve back to the northeast sets
up a prolonged heavy rain event across much of the area with 8 to 16
inches, locally 24 inches possible across southeast Mississippi,
portions of southwest Alabama and northwest Florida. This could be a
significant flood event. Moderate to major river flooding is also
likely. The high risk of rip currents continues into Thursday
morning. Although the remnants of Sally will be pulling well away
from the area Thursday into Friday, we will continue to see
scattered to numerous showers and thunderstorms through Friday with
a return to more typical rain chances by next weekend. /13
MARINE...Tropical Storm Sally (TS Sally), currently located over
the eastern Gulf of Mexico, will continue to slowly advance west-
northwest over the next few days and is forecast to strengthen to a
hurricane by Monday afternoon as it approaches the north-central
Gulf coast. At this time, TS Sally will slow in forward motion and
is still forecast to make landfall over far southeast Louisiana late
Monday night into early Tuesday morning. However, there still
remains uncertainty in the track and intensity of this storm. Thus,
impacts over the marine area will heavily depend on track and
intensity of the system. Tropical Storm Warnings remain in effect
for all of the Florida marine zones (including the Choctawhatchee
and Pensacola Bay systems). A Tropical Storm Warning and a Hurricane
Watch continues for the Alabama near shore Gulf waters, as well as
Mobile Bay and the Mississippi Sound. A Hurricane Warning is also in
effect for the Alabama Gulf waters beyond 20 nautical miles
offshore. Please refer to the latest Advisory from the National
Hurricane Center for the most current information regarding TS
Sally. /26
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Tropical Storm Warning for ALZ052-261>266.
Flash Flood Watch from 7 AM CDT Monday through Thursday morning
for ALZ051>056-059-261>266.
Storm Surge Warning for ALZ263>266.
Hurricane Watch for ALZ263>266.
High Rip Current Risk through Thursday morning for ALZ265-266.
High Surf Warning until 1 PM CDT Wednesday for ALZ265-266.
FL...Tropical Storm Warning for FLZ201>206.
Flash Flood Watch from 7 AM CDT Monday through Thursday morning
for FLZ201>206.
High Rip Current Risk through Thursday morning for FLZ202-204-
206.
Coastal Flood Advisory until 1 PM CDT Wednesday for FLZ202-204-
206.
High Surf Warning until 1 PM CDT Wednesday for FLZ202-204-206.
MS...Tropical Storm Warning for MSZ067-075-076-078-079.
Flash Flood Watch from 7 AM CDT Monday through Thursday morning
for MSZ067-075-076-078-079.
GM...Tropical Storm Warning for GMZ630>636-655-675.
Hurricane Watch for GMZ630>633.
Hurricane Warning for GMZ650-670.
&&
$$
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Area Forecast Discussion
National Weather Service Phoenix AZ
518 PM MST Sun Sep 13 2020
.UPDATE...Updated Fire Weather Discussion.
&&
.SYNOPSIS...
Slightly above normal temperatures are forecast this week with the
elevated haze from wildfire smoke likely to linger through early
this week. The warmest days will be near the middle of the week
with high temperatures topping out between 105-108 degrees across
the bulk of the lower deserts. Overall dry conditions are
expected, but slightly elevated moisture for early in the week
will support a slight chance of isolated afternoon showers and
thunderstorms primarily over high terrain areas and distant
deserts to the south.
&&
.DISCUSSION...
The strong Great Basin high pressure system has strengthened and
shifted further east and is now centered over the NE UT border with
a ~591 dam H5 center. A very weak mid to upper level trough axis is
positioned roughly east to west across the area with light winds
aloft. An H5 thermal trough also coexists with the weak trough
and extends northeast to a colder pocket over N NM. A 20:15Z ACARS
sounding indicated a PW of 0.75" which was up from 0.67" on the
Phx 12Z sounding due to an increase in moisture near 700 mb.
Early afternoon satellite imagery continues to show a large plume of
elevated smoke/haze continuing to drift into AZ from S CA and N
Baja. The layer of haze was reported by a pilot on approach to Sky
Harbor airport from about 14-15 Kft AGL at midday. Although the
layer of haze appeared to be creating a stronger overcast deck
than yesterday, today`s high has already reached 101 degrees by
early afternoon at Sky Harbor with regional temperatures running
several degrees warmer than yesterday in the upper 90s to low 100s.
Today`s highs should top out in the low 100s.
A gradual increase in regional tropical moisture from the south
and southeast will continue from now through the early part of
the week with PWs climbing just shy of 1" and closer to seasonal
norms. Combined with the weak UL low pressure disturbance that is
currently forming near the E AZ border through early to mid week,
expect a few relatively modest isolated showers and thunderstorms
across high terrain areas and the distant deserts to the south
today and every afternoon through Tuesday and possibly Wednesday.
The latest HREF CAMs guidance remain in good agreement on keeping
most of the convection during those periods rather isolated and
short-lived. Fleeting isolated showers for the Phoenix outskirts
through this period can not be ruled out either as suggested by
later runs of the HRRR. Gusty afternoon and evening outflow winds
with localized patchy blowing dust near any isolated showers and
storms will be the main concern.
Models remain in good agreement on maintaining the strong high
pressure system over the Southwest and West CONUS for much of the
week. The persistent regional high pressure will combine with a
drying trend beginning by midweek to support a warm-up as models
trend slightly warmer. Highs are expected to be several degrees
above normal for much of the week. Highs in and around Phoenix
could reach 105-108 by mid week and possibly a couple of degrees
warmer for SE CA to SW AZ. Although isolated areas of high heat
risk could develop, temperatures will remain significantly cooler
than more significant recent heat events.
Late this week and into the weekend a progressive low pressure
system passing to the north will flatten the ridge and shift it
south. Expect a slight cooling trend late this week and the weekend
as heights decrease. Mostly dry west-southwesterly flow aloft will
also manage to keep conditions dry along with some breeziness.
&&
.AVIATION...Updated at 0018Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light east to southeast winds are favored through the rest of the
afternoon with brief periods of variability. A southeast gradient
wind will strengthen to 25-30 kts above the surface after
midnight. The stronger winds should translate to the surface
later Monday morning around 15Z. Sustained winds around 10-13 kts
with gusts up to 16-20 kts will be possible through about 20Z
before subsiding. Winds should prevail out of the east through
Monday afternoon. In addition of the smoke layer aloft, FEW-SCT
cumulus around 10-12 kft AGL will develop again Monday afternoon,
with greater coverage than today. There will be a slight chance
for showers and storms Monday afternoon, but should remain focused
over the higher terrain to the north and east of Phoenix.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will remain very light through the TAF period, around 10
kts or less, with extended periods of variability. The partially
thin layer of smoke up around 20-25 kft AGL will persist through
the TAF period. Besides this skies should remain mostly free of
clouds.
&&
.FIRE WEATHER...
Wednesday through Sunday:
A generally warm and dry weather pattern is anticipated next week
with temperatures remaining slightly above normal. Mainly light
winds will favor normal diurnal patterns through the bulk of the
period. Daily min RH values will fall into the 10-15% range with
overnight recovery around 25-35% for lower elevations and 30-55%
for higher elevations. A very slight chance of an isolated shower
or thunderstorm will linger mostly for S Gila Cty on Wednesday
afternoon and evening.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Sawtelle
AVIATION...Benedict
FIRE WEATHER...Sawtelle/Kuhlman