Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Brownsville Texas
821 am CDT Friday Aug 29 2014
Discussion...due to low swells at the buoy with light to moderate
winds continuing...decided to cancelled the high risk of rip
current at the beaches this morning. Conditions will still be
favorable for moderate risk for today.
Previous discussion... /issued 722 am CDT Friday Aug 29 2014/
Discussion...updated for latest aviation discussion below.
Aviation...the aviation outlook for today will be pretty
problematic due to the presence of the weak surface low in place
over the region. The current conv has been hugging the coastline
throughout the overnight hours and has not made much progress
spreading into the lower rgv. The precipitable water values over the rgv remain
very elevated with a 00z value >2 inches with a pretty elevated
cape from last night. Will start off with VFR conditions initially
in the 12z taf set with mentions of vcsh/ts. Will mention some
tempo groups later today reducing ceilings and visibilities down to MVFR
levels by the afternoon hours. Will then transition the conv more
towards rain showers levels later this evening as the atms stabilizes
Previous discussion... /issued 358 am CDT Friday Aug 29 2014/
Short term /now through Saturday/...currently kbro radar shows an
area of conv firing over Kenedy County and extending down southeast
over the Lower Texas coastline into the offshore Gulf waters. The
cellular movement within this area is generally to the north-northwest with the
areal coverage gradually expanding over the last several hours. The
00z bro sounding showed a very healthy precipitable water of nearly 2.3 inches
with good cape values around 3650 j/kg. Surface observation indicate that
the weak surface low that was offshore may have pushed inland and
could be centered over the rgv early this morning. This surface low
will likely stay nearly stationary or will drift slowly west later
today through tonight and Saturday. This will likely keep the
eastern half of the bro County Warning Area on the more favorable side of the
surface low/trough which will provide a better environment for slow
moving heavy rain producing conv due to better surface convergence.
The conv potential throughout the short term will also be assisted
by broad weakness in the 500 mb ridge axis aloft which is expected
to linger over the Texas coastline into Saturday. Adding to this...both
the NAM and GFS forecast soundings show pretty deep layer tropical
moisture values persisting over the central and eastern half of the
bro County Warning Area with both models showing precipitable water values remaining well above
the 2 inch mark through Saturday.
So considering all of these factors...the main issue boils down to
how high of probability of precipitation to go with throughout the short term. The mav probability of precipitation
are a little lower in comparison to the wetter met and European model (ecmwf)
numbers. Will lean closer to the met and European model (ecmwf) probability of precipitation which appear to
have a little better handle on the timing and strength of the conv
Mulled over issuing an flash Flood Advisory for the eastern portions of the County Warning Area for
today but decided against it as soil moisture values remain pretty
low due to recent high temperatures and dry conditions. However will
continue to mention locally heavy rainfall possible throughout
today. An flash Flood Advisory may need to be reconsidered later tonight or Saturday
if the conv remains more widespread and stationary.
Temperature trends will hinge greatly on the conv coverage through Sat.
Considering the higher conv chances and cloud cover will go towards a
slightly cooler model consensus for both maxes and mins.
Long term /Saturday night through Friday/...
little change to inherited forecast...Bay of Campeche system next
week determines much of our weather.
Modest southeasterly low level flow will continue on Sunday which
should help limit precipitation potential in the afternoon despite abundant
low level moisture. Continued a 20 percent slight afternoon chance over
land which carried forward into Monday as middle level and ultimately
surface ridging begins to recenter more over Florida and Georgia
than over the north central Gulf of Mexico.
Late Monday into Tuesday a tropical wave enters the Bay of Campeche
and the best overall moisture values begin to move into the area as
low level flow over the Gulf of Mexico becomes more easterly. That
troughing/low pressure area depends on Wednesday and our easterly
flow becomes stronger. Continued a 30 percent pop basically from Tuesday
afternoon into Wednesday afternoon with all of the available
moisture. GFS remains more aggressive with the depth of the
troughing over the Bay of Campeche and uses the low pressure and the
interaction with ridging over Florida to create a long strong
easterly fetch over the Gulf. Discounted these wind speeds a bit
considering the possibility of tropical cyclogenesis in this area
which would create a much tighter windfield than the broad lumbering
low the GFS is suggesting. Prefer the European model (ecmwf) solution for now which
has a modest tropical wave moving slowly over the Bay before moving
inland on Thursday with the peak of 500mb vorticity south of here.
NHC continues to highlight this region in its tropical weather
outlook product as a low probability area and that appears justified
given the low shear/warm SST/ohc environment the wave/disturbance
will be entering. Its not scientifically possible to provide much
more at this time than ask everyone to remain aware of forecasts
over the next few days...particularly late this weekend into early
next week because cyclone or no cyclone could have implication on our
forecast even if we are not directly impacted.
Thursday into Friday middle level ridging shifts back westward and the
hot and dry southeasterly regime returns and precipitation chances steadily
begin to drop as high temperatures rise. /68-jgg/
now through Saturday...currently surface observation and buoy data
shows a light to moderate S-southeast surface flow continuing over the Bay
and Gulf waters early this morning with offshore seas holding around
4 feet. This light to moderate south to southeast surface flow will
likely persist into Saturday as the pgf remains fairly weak. This
should keep the Bay and Gulf conditions well below Small Craft Advisory criteria
throughout the short term.
Saturday night through Wednesday...
moderate southeast winds are forecast Monday and Tuesday to become
stronger and more easterly as low pressure forms in the southern
Gulf of Mexico/Bay of Campeche. Small Craft Advisory level winds
will become possible by Tuesday with seas becoming rougher due to a long
easterly fetch over the Gulf of Mexico. There is a small possibility
of tropical cyclone formation in the Bay of Campeche next week
and mariners are asked to remain alert to the latest forecasts
regarding this system.
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