Post by cycloneye on Nov 28, 2016 3:45:30 GMT -6
Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Mon Nov 28 2016
.SYNOPSIS...Base of mid to upper level trough now moving across Hispaniola
and quickly approaching the region will continue to create a southwesterly
winds flow and divergent pattern across the forecast areas today. This
deep layered trough is to reach the northern Leewards later tonight
or early Tuesday morning. A Broad surface trough extending northwards
across the region from the Eastern Caribbean, and old frontal
boundary/shear line northwest of the region, continued to induce
good low level moisture convergence and a south to southeast low
level wind flow. The low level trough is forecast to shift eastward
across the region and weaken by Tuesday, as High pressure builds
across the Western Atlantic and north of the region. This in turn
will increase the east to northeast trade wind flow during the
latter part of the work week.
&&
.DISCUSSION...The mid-upper level trough in combination with the
surface trough across the region will continue to increase instability
and provide good moisture transport across the local region today
through early Tuesday. This along with the favorable upper level
support will lead to continued shower activity and thunderstorm
development across the regional waters and portions of the islands
today. Showers and thunderstorms have already affected the local
waters and much of the islands with some enhanced convection already
noted over portions of the Mona Passage and just northwest and
north of Puerto Rico where frequent lightning was observed.
During the rest of the day, expect increased convection over land
areas with good potential for showers and thunderstorm development
with areas of locally heavy rainfall and strong gusty winds. Based
on the present and expected wind flow, the heaviest rainfall should
be focused across interior north and northeast portions of Puerto
Rico, as well as over the U.S Virgin islands where periods of locally
heavy rains can be expected.
By Tuesday afternoon and the remainder of the work week...as the
surface high pressure builds across the Western Atlantic and
across the region, expect increasing east to northeast trade
winds due to the tightening of the local pressure gradient. This
scenario will bring cool early morning showery rains to the north
coastal areas and east section of the islands along with cool
early morning temperatures across the region. As the high pressure
ridge gradually builds aloft, the chance for thunderstorm development
and enhanced convection will diminish and be suppressed by Tuesday and
the rest of the work week. Much drier conditions is so far expected
for the weekend based on recent model guidance and the overall weather
pattern.
&&
.AVIATION...SHRA/TSRA due to a sfc trof moving west to east across
the forecast area Today will create MVFR conds across most of the
terminals through at least 18z-20z. Mtn top obscd across PR and
brief IFR conds possible at the USVI/Leeward terminals between 12z-
18z. Bkn-ovc layers btw FL030-FL100. Sfc winds southeast around 10
kt with higher gusts near SHRA/TSRA. Winds bcmg east-northeast aft
29/00z.
&&
.MARINE...Showers and thunderstorms will produce hazardous marine
conditions across portions of the local waters during the rest of
the day. Expect seas up to 5 feet and winds up to 15 knots most
of today. However, expect increasing winds and seas by Tuesday
and during the rest of the week as the local pressure gradient
tightens and east to northeast trades winds increase. Small Craft
should exercise caution tonight, and small craft advisories will
likely be required for portions of the local waters by Tuesday
night.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 76 84 76 / 60 40 30 40
STT 84 74 86 76 / 60 40 40 20