Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Sun Aug 20 2023

Valid 12Z Sun Aug 20 2023 - 12Z Tue Aug 22 2023

...Heavy rains associated with tropical cyclone Hilary are likely to
produce catastrophic to life-threatening flooding over portions of the
Southwest...

...Dangerous heat to continue to expand across the central U.S. through
the early part of this week...

...Potentially heavy rain moving into southern Texas on Tuesday...

Hurricane Hilary continues to move north in the eastern Pacific near the
coast of Baja California this morning.  Rain associated with the system
has been spreading north across portions of southern California and
western Arizona into the Great Basin overnight and is likely to increase
in intensity later today as the storm continues its northward track. 
Moisture-laden southerly winds are expected to support very heavy
rainfall, with some locations likely to accumulate rainfall totals
exceeding their typical annual amounts in just a matter of hours.  This
potentially historic rainfall is expected to cause flash, urban, and
arroyo flooding, including landslides, mudslides, and debris flows.  These
dangerous to catastrophic flooding impacts are expected to occur today
through early Monday.  WPC continues to highlight parts of southern
California into southern and central Nevada as the area where the threat
for numerous to widespread flash flooding is most likely. 

In addition to heavy rain, tropical storms conditions are expected to
begin today across portions of southern California.  Winds could be
particularly strong and gusty in and near areas of higher terrain.  Large
swells will affect portions of southern California over the next couple of
days.  These swells are likely to cause life-threatening surf and rip
current conditions.

Hilary will quickly weaken as it moves into the interior Southwest
tonight.  However, ample moisture will remain, supporting widespread
showers and thunderstorms from the Southwest through the Intermountain
West into the northern Rockies on Monday.  These storms will have to the
potential to produce additional heavy rainfall amounts and flooding
concerns.  Strong and gusty winds will remain a threat as well for parts
of the central and northern Intermountain West, especially along the
higher terrain.

Dangerous heat already impacting portions of the central and southern
Plains and the lower Mississippi Valley will continue to expand, with well
above-normal and record-breaking temperature spreading across the mid
Mississippi Valley today.   On Monday, the heat will begin to spread back
into the northern Plains and upper Midwest, where it will likely remain
entrenched into midweek.  The prolonged nature of the heat wave, combined
with very warm overnight temperatures will offer limited relief from the
oppressive daytime heat -- compounding the overall heat impacts.

Along the Gulf Coast, an area of disturbed weather is expected to move
west into the Gulf of Mexico later today.  This system is forecast to move
steadily across the Gulf, nearing the Texas coast early Tuesday.  NHC is
monitoring this system, noting a tropical depression may form as it
approaches the coast.  Regardless of development, the threat for heavy
rainfall is expected to increase across southern Texas beginning late in
the period.

Much of the eastern U.S. is forecast to remain dry through the period. 
Daily showers and thunderstorms are expected across Florida and along the
Southeast coast.  Also, some light rain may accompany a cold front pushing
south across the Northeast on Monday.  Above-normal temperatures are
expected to return to much of the eastern U.S. over the next two days,
then cooler temperatures will begin to spread across the Northeast behind
the cold front on Tuesday. 

Pereira

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php