Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
250 PM AST Wednesday Jul 29 2015
TUTT low now centered overhead will continue to retrogress during
the remainder of the week. A tropical wave with axis just east of
the Lesser Antilles...will enter the eastern Caribbean overnight.
The tropical wave will then move across the regional waters on
Thursday and Friday...while transporting a surge of tropical
moisture which will interact with the TUTT low already in place
across the region.
Discussion... few showers were noted forming over portions of
the west interior and the coastal waters between eastern Puerto
Rico and the northern Virgin Islands. Overall...dry weather conditions
prevailed across the entire region as the Saharan air layer smothered
the region and continued to limit convective development. Still expect
a few more showers may form during the rest of the afternoon...but
activity will be of short duration and limited only to portions of
the interior sections of Puerto Rico. A gradual clearing is expected
over land during the overnight hours.
Latest water vapor and visible satellite images showed well
defined TUTT low across the region. This feature will continue
westward across the forecast area through Thursday. Model guidance
continued to place the upper low in a favorable area for upper
level instability late Thursday through Friday. This along with
the surge of tropical moisture being transported by the tropical
wave...will allow for better convective development with enhanced
showers and thunderstorms across the islands and coastal waters.
Latest layered precipitable water products continued to suggest
precipitable water values reaching 2.00 inches of so by Friday across the
forecast area. By Saturday...rapid drying is expected as TUTT low
weakens aloft and shifts farther west...and another area of dry
Saharan air will move across the region. By Monday...another
tropical wave is expected to move across the region but no
significant amounts of rainfall is so far expected.
Aviation...VFR conds expected across the local islands. Vcsh
possible for tist/tisx and tjsj early in the afternoon with thunderstorms in the vicinity
possible at tjmz after 29/17z. Easterly winds around 15 kts with sea
breeze variations...diminishing to 5-10 knots after 30/00z. Vcsh
possible across tncm/tkpk...tist/tisx as well as tjsj after 30/06z.
Marine...seas up to 5 feet and winds 10 to 15 knots during the overnight
hours...then occasionally up to 6 feet mainly offshore by late Thursday
and Friday with increasing trade winds up to 20 knots...as a tropical
wave is expected to move across the regional waters. Please refer
to the latest coastal waters forecast issued by the National Weather
Service weather forecast office San Juan PR for updates and additional information.
Preliminary point temps/pops...
sju 79 90 78 87 / 10 30 20 40
stt 78 89 78 87 / 30 30 30 30