Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
324 PM AST Monday Jul 27 2015
Synopsis...a middle to upper level ridge continued in place across the
Atlantic and will dominate the local weather pattern at least through
Tuesday. Strong surface high pressure will remain in place across
the southwest and central Atlantic. This will help to maintain moderate
easterly trade winds across the region for most of the week. A tropical
wave is forecast to enter the eastern Caribbean by middle week...then move
across the regional waters on Thursday.
Discussion...hot and hazy conditions prevailed across the region
today with limited showers activity...as a strong cap inversion
and and the presence of Saharan dust limited convective development.
Expect mostly clear skies and hazy conditions during overnight hours
and on Tuesday. Some light passing showers may move across the local
waters but no significant rainfall amounts are expected over land.
At least until Wednesday and Thursday...expect fairly dry and stable
conditions due to the middle to upper level ridging... limited moisture
advection...and the presence of Saharan dust particulates.
Afternoon convection if any will be focused mainly over sections
of western Puerto Rico. Lesser chance for showers expected over
the Virgin Islands on Tuesday.
By Wednesday...ridge aloft is to gradually erode as an upper level
low/TUTT will relocate westward across the region Wednesday through
Thursday. Latest satellite imagery and naaps aerosol product continued
to suggest the Saharan air layer was now spread across the region...
with the highest concentration of suspended Saharan dust to affect
the region today through Tuesday...then gradually diminish by middle
A tropical wave is expected to reach the eastern Caribbean late
Wednesday...then move across the area on Thursday. This along with
the repositioning of the TUTT low aloft will help create upper level
instability...and therefore increase the chance for showers and
thunderstorms during the latter part of the work week. Models
however still suggest...drier conditions will quickly return by
the weekend as the Saharan air layer will again move over the
Aviation...VFR conds expected across the local terminals. Rain showers
expected in and around tjmz through 27/21z. Only a slight chance of
brief rain showers across the local area overnight...therefore brief vcsh is
possible across tist/tisx as well as tjsj. Suspended Saharan dust
present over the area but visibility expected to remain p6sm.
Easterly winds with sea breeze variations at around 15-20 kts and
gusty through rest of the day...gradually diminishing to around
5-10 kts after 28/00z into the overnight hours. Winds increasing
again to around 15 knots after 28/13z.
Marine...winds up to 20 knots and local seas up to 6 feet. Small craft
should exercise caution across most of the local waters overnight
Preliminary point temps/pops...
sju 78 89 79 89 / 10 20 20 20
stt 80 90 79 89 / 20 20 20 20