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FOUS30 KWBC 180829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Tue Jun 18 2024

Day 1
Valid 12Z Tue Jun 18 2024 - 12Z Wed Jun 19 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE UPPER AND
MIDDLE TEXAS COASTS...

...Upper and Middle Texas Coasts...

Potential Tropical Cyclone 1 (PTC1) will continue to organize
across the southern and western Gulf today. Associated moisture
originating in the Caribbean will stream northwestward into the
Texas coast around the northern and eastern periphery of the
storm. IVT values are very impressive...building to the upper end
of the scale at 1,500 kg/m/s. This means PWATs with the storm will
consistently increase through the day, approaching 3 inches by the
time the storm`s full brunt moves into the coast tonight. PWATs
approaching 3 inches mean the atmosphere will be carrying about as
much moisture as it can possibly carry...and storms that form in
this environment will be capable of extremely heavy rainfall rates
due to highly efficient rainfall processes. Moisture lost by the
rainfall will be quickly replaced as moisture advection (signified
by the extremely high IVT values) will be optimal.

All of this to say, as the plume of moisture associated with PTC1
and supported by advection straight out of the Caribbean moves into
the upper Texas coast tonight, it will contain convection capable
of 3 inch per hour rainfall rates. These rates will easily
overwhelm local streams and creeks as they track northwestward, no
matter how dry/empty they were prior to the start of the rain. This
will likely catch many off guard, so it`s important to avoid
crossing flooded roadways.

With the better-forecast organization of PTC1, it`s expected that
the associated plume of moisture and heavy rainfall will be more
consolidated as it approaches the Texas coast as compared with
previous forecasts. This means the timing of the heavy rainfall has
been slightly delayed, and is less likely to extend too far north
from the coast. Thus...the inherited ERO risk areas have been
trimmed from the north from inherited. It`s likely that it will
take until after 06Z tonight before consistent and steady heavy
rainfall begins moving into the coast, with only scattered
convection expected prior to that.



***The rest of this discussion will be updated shortly. Thank you
 for your patience.***

Wegman

Day 2
Valid 12Z Wed Jun 19 2024 - 12Z Thu Jun 20 2024

This discussion will be updated shortly. Thank you for your
patience.

Wegman

Day 3
Valid 12Z Thu Jun 20 2024 - 12Z Fri Jun 21 2024

This discussion will be updated shortly. Thank you for your
patience.


Wegman


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt