FXUS64 KMOB 240209 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
909 PM CDT Wed Aug 23 2017

.DISCUSSION...See updated information for land areas below.


.UPDATE...Radar imagery shows scattered showers and thunderstorms
continue to develop along a weak cold front moving slowly south
across northern portions of the area. Due to the slow movement of
the storms, heavy rainfall will continue to be the main threat
along with frequent cloud to ground lightning. The showers and
thunderstorms will continue to weaken through the late evening as
the boundary layer cools. The current forecast remains on track
and no significant updates are needed at this time. /13


.PREV DISCUSSION... /issued 638 PM CDT Wed Aug 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...VCTS will gradually dissipate this evening with
VFR conditions expected overnight. VFR conditions will prevail in
most areas on Thursday, except for MVFR to IFR conditions in and
around scattered showers and thunderstorms. /13

PREV DISCUSSION... /issued 403 PM CDT Wed Aug 23 2017/

NEAR TERM /Now Through Thursday/...Sfc to h5 ridge of high
pressure over the eastern and north central Gulf of Mexico
stretching north over the north central gulf and se states will
begin to break down from west to east tonight and on thu in
response to Tropical Depression Harvey entering the sw Gulf and
Bay of Campeche. To the north a broad upper trof mostly over
Appalachians and Eastern conus will continue to slowly shift
eastward through thu afternoon. In the wake of the upper trof to
the north a weak frontal boundary is noted pushing down across
lower parts of Al and Ms and possibly just north of the NWFL coast
by early Thu morning leading to slightly drier/cooler conditions
at the surface across most of the northern half of the forecast
area on Thu. a light northerly wind at the surface for most
locations in the morning will also make conditions feel almost
fall like through about mid morning. Less coverage of showers and
thunderstorms can also be expected overnight near the coast and
offshore and over interior sections of the forecast area during
the day on Thu due to less forcing aloft and more stable
conditions in the boundary layer beginning later this evening
continuing through Thu afternoon. Model soundings reflect these
lower values on Thu with pwats dropping below 2 inches across most
of the northern half of the forecast area with a warm nose also
showing around 9k ft in most of the model soundings in the area.
For the rest of today and this evening showers and thunderstorms
will form out ahead of the weak front boundary and move south
towards the coast. With moderate instability combined with mid to
upper lapse rates mostly above 6.0 c/km a few strong storms will
still be possible later this afternoon and early this evening.
Gusty straight line winds possibly up to 40 mph or slightly
better, very heavy rain and frequent cloud to ground lightning
will be the main threats with the stronger storms through early
this evening.

As mentioned above temperatures will be slightly cooler tonight
especially over the northern and western locations ranging from the
upper 60s to lower 70s, and the middle 70s further south to the
immediate coast. Highs Thu will be near seasonal averages ranging
from the upper 80s to lower 90s for all locations. 32/ee

SHORT TERM /Thursday night Through Saturday night/...Harvey is
forecast to continue tracking northwest over the southwest Gulf of
Mexico, and make landfall along the Texas coast late in the week.
Meanwhile, a weak upper level trough should remain over the
eastern conus. Will continue with the upward trend toward higher
precipitation chances from isolated to scattered on Friday to
scattered to numerous on Saturday. There is at least some
potential for a heavy rain and frequent lightning to occur with
the stronger storms. In addition, an increase in long period
swells across the coastal waters Friday and into the weekend
should lead to an increased rip current threat along area beaches.

High temperatures Friday will range from 87 to 93 degrees, and
from 84 to 87 degrees on Saturday. Low temperatures will be close
to normal, ranging from 69 to 73 degrees inland areas, with mid
70s along the coastal sections. /22

LONG TERM /Sunday Through Wednesday/...Impacts across the
forecast area in the long term remain largely dependent on the
track and size of Harvey. For now, anticipate that the system will
remain west of the area through the middle of next week, but that
would still place us in the eastern quadrants that have the
potential to produce the most rain and tornadoes. However, this
far out there is still much uncertainty, but will continue the
trend toward high precipitation chances (scattered to numerous)
throughout the long term. There is at least some potential for a
heavy rain and or severe weather event to occur over the forecast
area during the Monday through midweek timeframe. Long period
swells will likley remain across the coastal waters, keeping an
elevated rip current threat along area beaches.

Due to the expected increased in overall cloud coverage and high
rain chances, high temperatures Sunday through Wednesday will be
about 5 to 10 degrees below normal, ranging from 80 to 85 degrees.
Low temperatures will be close to normal through the long term,
ranging from 67 to 72 degrees inland areas, with mid 70s along the
coastal sections. /22

MARINE...High pressure over the north central gulf will weaken
from west to east for the remainder of the week in response to
Tropical Depression Harvey tracking northward over the western Gulf.
As a result increased swell from Harvey will begin to propagate east
and north over the north central Gulf and marine area later in the
week and over the weekend, and into next week. A light southwest
flow this afternoon will shift north then build slightly overnight
and early Thu, then shift northeast to east and diminish later in
the day. Easterly winds and seas will begin to build on Fri and
continue through early next week as Harvey continues to move slowly
northward over the extreme westerly Gulf. All marine interests
should stay tuned to the National Hurricane Center and their local
forecast office in Mobile Al for further updates on the forecast
track of Harvey and its impacts later in the week and over the
weekend, continuing into next week. 32/ee




This product is also available on the web at:

NWS MOB Office Area Forecast Discussion