Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 250805
Area Forecast Discussion
National Weather Service San Juan PR
405 AM AST Tue Oct 25 2016
.SYNOPSIS...Short-wave upper level trough over Hispanola will move
westward over the region today. This trough aloft combined with
the proximity of the shearline/pre-frontal trough will enhance the
moisture convergence across the local islands through Thursday.
Mid to upper level ridge will build over the region from Friday
through the weekend...limiting the showers and thunderstorm
coverage across the local islands.
.DISCUSSION...Moist and unstable conditions will continue to
prevail across the forecast area under the influence of the upper
level trough and the shearline/pre-frontal trough. Although...the
frontal boundary will remain far northeast of the local area, the
shearline will continue to affect the local weather conditions
over the next couple of days.
Today and tonight...East-northeast winds at low levels will
continue to favor passing showers across the coastal waters and
portions of the north and east coastal sections of the islands
this morning. Then...afternoon convection will be likely once
again across the Central Interior...West...Southwest and South
Central Puerto Rico. The soils across these areas are fairly
saturated and rivers/streams are running high...therefore any
additional heavy rainfall will result in urban and small stream
flooding especially late in the afternoon.
The rest of the week...environmental conditions remain favorable
for shower and thunderstorm activity through Thursday. Therefore...
expect passing showers affecting the windward areas of PR and USVI
at night and early in the morning...followed by a few rounds of
convection across the Western half of PR each afternoon. Conditions
will gradually improve from Friday into the upcoming weekend as a
mid-upper level ridge builds over the forecast area. This dry and
more stable air mass will result in less shower and thunderstorm
coverage across the local islands later in the week.
Unstable pattern is possible again by midweek next week when an
upper level trough amplifies over the Western Atlantic.
.AVIATION...Mainly VFR conds expected across much of the forecast
period. However, trade wind showers on ENE wind flow could reach
portions of the nrn leewards/USVI and east/northeast PR thru 14z.
Then between 16z-22z, SHRA/TSRA will develop over and downwind of
the Central Mtn ranges of PR. Brief MVFR expected at TJMZ/TJPS.
Also, streamers developing off the USVI could result in brief MVFR
conds during the afternoon hours. SFC winds ENE at 5-15 kt. Sea
breeze variations aft 14z.
.MARINE...Tranquil marine conditions will continue to prevail
with seas up to 4 feet and winds 10 knots or less except in the
Atlantic Offshore waters and passages where winds will be 10 to 15
knots and seas up to 5 feet. No Small Craft Advisories are
anticipated the rest of the week.
.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 88 78 / 50 50 30 40
STT 87 78 87 78 / 50 50 30 40