Tropical Storm Beta Discussion Number 10
NWS National Hurricane Center Miami FL AL222020
1000 PM CDT Sat Sep 19 2020
Beta's deep convection has been waning this evening. An Air Force
Reserve Hurricane Hunter aircraft has found that the central
pressure rose several millibars since this morning, but the plane
also still measured surface winds around 50 kt from the SFMR
instrument. The strongest winds appear to be located near on old
frontal boundary which extends north and east of Beta's center, and
in fact sustained tropical-storm-force winds are just grazing the
coast of south-central Louisiana.
The aircraft fixes indicated that Beta drifted north-northeastward
during the day. Right now, the cyclone is embedded within weak
steering currents between two areas of high pressure centered near
the Bahamas and west Texas/southern New Mexico. The western high
pressure area is expected to slide eastward across the Southern
Plains into the southeastern U.S. through Sunday night, which should
force Beta to move slowly toward the west-northwest toward the Texas
coast. The center is now expected to reach the coast between 48-60
hours, at which point it is likely to recurve around the mid-level
high and move slowly northeastward near or inland of the upper
Texas coast on days 3 and 4. Because of Beta's drift today, the
new guidance envelope has shifted a bit northward. For this
forecast cycle, the NHC official forecast split the difference
between the previous interpolated forecast and the HFIP Corrected
Consensus guidance. This keeps the forecast to the east of the
ECMWF, HCCA, and TVCN multi-model consensus during Beta's slow
recurvature.
The air mass behind the old front appears to have won out. Beta's
circulation is embedded in a dry environment of mid-level
relative humidities around 50 percent, and the air mass could
actually become more stable as Beta moves closer to the Texas
coast. On top of that, the moderate southwesterly shear is not
expected to diminish much at all. As a result, the intensity
guidance has continued to trend downward, and the new official
forecast now flatlines Beta's intensity at 50 kt until landfall
soon after 48 hours. This forecast still lies near the top end of
the guidance envelope, closest to the SHIPS model. After 48 hours,
weakening is expected assuming Beta's center remains over land, and
it is now expected to become a remnant low over Louisiana by day 5.
While the chances that Beta will become a hurricane continue to
decrease, the Hurricane Watch for portions of the coast of Texas are
being maintained out of an abundance of caution given the
uncertainty in the forecast.
Key Messages:
1. The expected slow motion of Beta has the potential to expand a
long duration rainfall event from the Louisiana coast westward into
southeast Texas on Sunday and northward into the Mid-South by mid
next week. The potentially prolonged period of rainfall could cause
flash, urban, and river flooding, especially where tide levels are
above normal.
2. There is the danger of life-threatening storm surge near times of
high tide from Sunday through Tuesday along portions of the Texas
and Louisiana coasts within the storm surge warning areas.
Residents in these areas should follow advice given by local
officials.
3. Tropical storm force winds are expected to begin along portions
of the northwestern Gulf Coast overnight within the tropical storm
warning area in Louisiana and will spread westward to the Texas
coast Sunday through Monday. Hurricane-force winds are possible
along portions of the Texas coast late Monday and Monday night,
where a hurricane watch is in effect.
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