639
FXUS64 KHUN 262322
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
622 PM CDT Thu Sep 26 2024

...New AVIATION...

.NEAR TERM...
(Tonight)
Issued at 312 PM CDT Thu Sep 26 2024

Hurricane Helene has strengthened to a major hurricane this
afternoon with the new 1 PM CDT Advisory issuance. Minimum central
pressure has dropped to 959 mb with maximum sustained winds of 110
mph. It was located 195 miles southwest of Tampa, Florida and
moving to the NNE at 16 mph at 1 PM CDT. It is still expected to
make landfall in the Big Bend area of Florida. Wobbles in the
track to the east or west could still effect the eventual landfall
location.

A cold front continues to remain in place over the western Florida
panhandle extending NNE into the north central portions of
Georgia. This has helped trend the movement of Helene a bit
further east than its previous movement. When and how much Helene
turns more to the north will have a big impact on just how heavy
and how far westward into Alabama heaviest rainfall progresses
into tonight and Friday morning. A thunderstorm or two could
occur, but they shouldn`t be strong this evening into Friday
morning.

Either way, the front is not expected to move much, so it will be
a focusing mechanism for training of heavy tropical rainfall
rates. This should mainly occur east of the I-65 corridor and
into southern middle Tennessee, where post-frontal lift and
highest moisture content provide the greatest potential for heavy
persistent rainfall. Some gusts around 40 mph are possible as the
western edge of the weakening tropical system approaches NE
Alabama towards daybreak on Friday. These will likely continue
into the day as the weakening (likely a tropical depression) moves
west across central Tennessee. These gusts may need to be revised
a bit higher in future updates (especially if we can mix up to 50
knots of wind Friday afternoon at 850 mb). There is some spread
in 850 mb wind speeds, so kept highest gusts around 40 mph for
now. A Wind Advisory has been continued that starts at 1 AM CDT on
Friday and has been extended westward across the entire area
through 1 AM CDT on Saturday. The heaviest rainfall will likely
occur this evening to around daybreak on Friday. Expect that to be
the main threat for flash flooding to occur.

&&

.SHORT TERM...
(Friday through Sunday)
Issued at 312 PM CDT Thu Sep 26 2024

However, additional flash flooding and river flooding though
could occur into the day on Friday. Thus, a flood watch remains in
effect from 1 am CDT on Friday through 1 AM CDT on Saturday. Guidance
is showing the energy from the remnant of Helene being absorbed
into a upper low along/just behind the front. Some additional
moderate to heavy rainfall could linger flash flooding and areal
flooding to 1 AM CDT on Saturday. Thus, the flood watch was
extended through that time.

There should be a good gradient in rainfall totals in a transition
zone from NW Alabama further NE across the remainder of the area.
One to three inches looks more likely in NW Alabama, with the
higher amounts more likely further northeast between 3 and 5
inches with some isolated higher amounts around 7 inches possible
through Saturday morning. Flash and areal flooding concerns should
ease Saturday afternoon into Saturday night.

&&

.LONG TERM...
(Sunday night through Thursday)
Issued at 312 PM CDT Thu Sep 26 2024

Global models suggest that the deep-layer cyclone to our north
will continue to lift slowly northeastward on Sunday night, with
SW flow to the east of a trailing trough axis maintaining a moist
airmass across the TN Valley. It appears as if the drying trend
aloft will be complemented by a drying trend in the low-levels by
the middle of next week, as a cold front tracks southeastward
through the TN Valley. Although the cold front may indeed advect a
drier continental airmass into the region, highs will warm back
into the l-m 80s by Tuesday/Wednesday due to abundant sunshine
each afternoon. A dry forecast may return by next week.

&&

.AVIATION...
(00Z TAFS)
Issued at 622 PM CDT Thu Sep 26 2024

VFR conditions are forecast to continue, but will be short-lived
as Helene begins to make local impacts to our area overnight. IFR
to MVFR conditions are forecast to move in overnight into the
early morning hours as ceilings and visibilities drop at both
KMSL and KHSV. By 11Z, MVFR conditions are forecast to prevail
with a low chance of IFR conditions due to continued lowered
ceilings and visibilities as showers move over the area. In
addition to this, gusty winds are forecast to become prevalent
with gusts up to 22 kts from the northwest, which will increase in
speed (up to 35 kts) and become southwesterly by the end of the
TAF period. A low chance of LIFR conditions exists by the end of
the TAF period as ceilings could drop as low as 400 ft accompanied
by visibilities around 2SM.


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Flood Watch through late Friday night for ALZ001>010-016.

     Wind Advisory from 1 AM Friday to 1 AM CDT Saturday for
     ALZ001>010-016.

TN...Flood Watch through late Friday night for TNZ076-096-097.

     Wind Advisory from 1 AM Friday to 1 AM CDT Saturday for TNZ076-
     096-097.

&&

$$

NEAR TERM...KTW
SHORT TERM....KTW
LONG TERM....KTW
AVIATION...HC