Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 271900
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
200 PM CDT Tue Oct 27 2020

.UPDATE...
Midday Update.

&&

.SHORT TERM...
/Updated at 0158 PM CDT Tue Oct 27 2020/

Through this Afternoon.

A mid-level ridge is situated just north of the Bahamas this
afternoon with TS Zeta emerging from the Yucatan Peninsula into the
southern Gulf of Mexico. Surface winds are slowly becoming aligned
with the southerly winds aloft and driving an increase in moisture
across Central AL. Dewpoints have risen into the upper 60s to near
70 and will rise another degree or two through the day, and the
stratus layer will settle in for the next 24 hours. A lingering
front remains situated across the northwestern portion of the state
reinforced by wedging as a result of easterly surface winds. Showers
have begun to develop along the coastal areas and will move
northward into our south later this afternoon/evening supported by
strong isentropic lift.

Tonight through Tomorrow.

The band of showers will lift northward overnight and near I-20 by
sunrise. Behind the convergent boundary, most of the area will stay
dry for the later half of the morning. Meanwhile, Zeta will make
quick approach towards the Louisiana coastline while an upper low
moves eastward into the Lower Plains states. Zeta will begin a
northeastward shift as it comes under influence of strong
southwesterly winds associated with the upper low. We will begin to
see coverage of showers and thunderstorms increasing across the
western half of the state by early afternoon and becoming numerous
to widespread heading into Wednesday evening as Zeta makes landfall
and begins to accelerate inland. Central Alabama impacts from Zeta
will be detailed in the long term discussion.

86

.LONG TERM...
/Updated at 0437 AM CDT Tue Oct 27 2020/

Wednesday night through Thursday night:

Zeta has temporarily weakened to a tropical storm after making
landfall along the Yucatan Peninsula but is expected to restrengthen
to a hurricane once it moves back over the warm Gulf waters later
today. Southerly steering flow between a subtropical ridge centered
near the Bahamas and an upper low drifting eastward across New
Mexico and West Texas will cause Zeta to move northward, making
landfall over southeast Louisiana Wednesday evening at or near
hurricane strength. Depending on its exact track, the center may
briefly move over water again before another landfall along the
Mississippi Gulf Coast. Strengthening flow ahead of the upper low
will cause Zeta to accelerate northeastward across Central Alabama
Wednesday night, reaching the Mid-Atlantic by Wednesday afternoon. A
mid-level dry slot associated with the upper low will quickly put an
end to precipitation across the area on Thursday. A cold front will
move through in the afternoon, with temperatures in West Alabama
falling during the afternoon. Some wraparound moisture associated
with the upper low moves in across the north Thursday night which
may result in additional light showers/drizzle.

IMPACTS:

Winds: Wind is starting to look like the main impact from this
system. While we would normally not be as worried about high wind
potential for a system barely at hurricane strength making landfall
where it is, this system will be very fast-moving. There will also
be a strong pressure gradient/fall-rise couplet as it moves through
due to its strong size. Several models, including the GFS, ECMWF,
and the HWRF and HMON hurricane models indicate very strong winds
just above the surface (90 kts at 850 mb and 75 kts at 925mb). While
low-level stability will prevent efficient mixing of these higher
values to the surface, there will still likely be some mechanical
mixing. With these low-level wind fields, there is increasing
concern that 50 to 60 mph wind gusts could be realized at the
surface, especially in some of our southern counties. While
sustained winds would likely be below tropical storm force, the
potential impacts of these wind gusts knocking down numerous trees
warrants a tropical storm watch for some of our southern
counties. It`s possible this could be expanded northeastward in
later updates. A wind advisory will certainly eventually be needed
for areas not in a watch/warning. Models indicate the wind field
will be very asymmetric with the highest winds confined to areas
along and to the right of the center.

Flooding:

Rainfall amounts have trended upward, though the fast motion of
the system remains a limiting factor. A swath of 2 to 4 inches of
rain is forecast. While widespread flooding is not expected, some
localized flash flooding will be possible Wednesday night
especially in urban areas and areas that received rainfall on
Saturday. Will also have to watch how much rainfall falls tonight
and tomorrow ahead of the main core of rain with the system. With
the heavier rain coming beyond 36 hours from now, and marginal
rainfall amounts, will not be issuing a flash flood watch at this
time.

Tornadoes:

The very strong low-level wind fields will result in strong to
extreme low-level SRH and hodographs. However, instability
continues to look meager due to the overnight timing and easterly
winds ahead of the system. Have kept in the marginal risk for now
but did trim a little of the northern edge.

Friday through Monday:

Cooler and drier conditions are expected. Another cold front moves
in Sunday but moisture return appears to limited for precipitation
at this time.

32/Davis

&&

.AVIATION...
18Z TAF Discussion.

IFR ceilings remain present across the area this afternoon, but are
slowly rising. With easterly surface winds transitioning to
southerly aloft, the stratus layer will remain in place through the
TAF period. Guidance indicates ceilings should rise above 3kft this
afternoon, but this process has been slow up to this point. VFR
criteria may only last for a few hours this afternoon before rain
moves inland towards the southern terminals this evening ahead of
surging Gulf moisture which will be lifted by a lingering wedge
front. Expect ceilings to drop to IFR again around midnight for the
remainder of the TAF period with main flight impacts associated with
the band of northward moving showers. Surface winds become
southeasterly tomorrow morning as tropical system Zeta moves into
the northern Gulf of Mexico, but not expecting any mentionable wind
gusts in this TAF period.

86


&&

.FIRE WEATHER...

Moisture will increase today ahead of an approaching tropical
system. Showers and isolated thunderstorms will begin to move in
from the south through the afternoon, becoming more numerous across
the area tonight and Wednesday. Widespread rain, heavy at times,
will move through Wednesday night into Thursday morning as tropical
system Zeta moves through along with strong winds. Drier and cooler
conditions will return to the area Thursday night and remain through
the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     66  75  69  75  48 /  70  70  90  70  20
Anniston    70  76  70  77  50 /  70  60 100  70  10
Birmingham  69  77  70  76  50 /  70  70 100  70  10
Tuscaloosa  71  78  70  76  49 /  70  80 100  60  10
Calera      70  77  69  75  49 /  70  70 100  70  10
Auburn      69  76  71  76  51 /  60  50  80  70  10
Montgomery  72  81  73  80  51 /  70  60  90  60  10
Troy        72  81  73  81  51 /  60  50  70  60   0

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Tropical Storm Watch for the following counties: Autauga...
Chilton...Coosa...Dallas...Elmore...Lowndes...Marengo...
Montgomery...Perry.

&&

$$



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