Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
136 PM AST Sat Aug 27 2016
Synopsis...Tropical Storm Gaston well northeast of the region
across the central Atlantic...and the broad area of low pressure
with associated tropical wave extending across the western Caribbean
and the southwest Atlantic, will continue to induce a moist southeast
wind flow across the region through the rest of the weekend. Weakening
high pressure ridge aloft will shift westward over the next few days
as a TUTT low will retrogress westward and reach the northeastern Caribbean
later today and Sunday.
Discussion...the moist southeasterly wind flow and upper level
diffluence along with local and diurnal effects will continue to
provide good instability and upper level support for the formation
of showers and thunderstorms across the region during the afternoon
and early evening hours. Some of the activity will be enhanced and
may lead to Urban and Small Stream flooding. The afternoon convection
should diminish over land during the early evening leaving variably
cloudy to partly cloudy skies. By early morning however the dominant
southeast wind flow and proximity of the upper low will again enhance
shower development over the coastal waters and bring periods of passing
showers to east and southeast portions of the islands. Some showers
thunderstorms may produce brief periods of moderate to locally heavy
For the remainder of the day on Sunday and through Monday...a
TUTT induced low level trough will move across the area in tandem
with the TUTT low which is forecast to move across the northeastern
Caribbean and local region. This along with the still fairly moist
southeast wind flow will give way to additional showers and isolated
thunderstorms. Some of the activity will be locally enhanced across
parts of the interior and northern half of PR including parts of
the San Juan Metro area.
Based on the latest model guidance and recent satellite imagery, conditions
are expected to gradually improve by Tuesday as moisture convergence
will diminish across the region, and winds will become more easterly
in response to a surface high pressure ridge building just north of
the forecast area.
Aviation...mostly VFR conditions expected over most taf sites...however
isold tstms will affect vcnty of tjps/tjsj/tjbq and tjmz through 27/23z.
A few shwrs/tstms could result in mountain top obscuration across the
Cordillera Central of PR through this evening. Low level winds will
be mainly east at 10 to 15 kts with higher gusts mainly with isold tstms.
Marine...a small but long east-northeast swell, generated by tropical cyclone Gaston is
will continue to affect the local Atlantic waters and Anegada overnight
through Sunday. Isolated thunderstorms with areas of locally heavy rainfall
and dangerous lightning will remain possible across the regional waters
through the late evening hours.
Preliminary point temps/pops...
sju 79 90 79 90 / 30 40 20 30
stt 82 89 82 88 / 40 40 30 30