National Weather Service San Juan PR
509 AM AST Wed Nov 30 2016
.SYNOPSIS...Strong mid to upper leve ridge extends across the
Greater Antilles from the Central and Eastern caribbean into the
West Atlantic. Meanwhile, A short wave trough extends from the
Central Atlantic southwards across the Lesser Antilles with an
area of low pressure across the Northern Leewards. The mid to
upper level ridge is to build across the region today through the
end of the week, as the trough and associated low sinks farther
south and fills/weakens. This in turn will strengthen the trade
winds and cap inversion.
In the low levels...The induced mid to low level trough is supported
by a broad inverted surface trough spread across the Eastern Caribbean.
This trough extends northwards across the region with a weakly embedded
low now centered just northeast of the northern leewards. This trough
and associated low is forecast to shift west southwest across the region
through wednesday while slowly weakening as surface high pressure ridge
builds north of the forecast area.
&&
.DISCUSSION...
For the rest of the early morning hours,fragments of shallow low
level moisture, remnants from old frontal boundaries and shear
line just north of the region move across the forecast area in the
prevailing moderate northeast trade wind flow. This prevailing
wind flow is induced by the high pressure ridging north of region
and low circulation just NE of area. Skies are to then become
mostly sunny by late morning and the rest of the day. However,
expect some additional afternoon cloudiness and showers of mainly
of light to moderate intensity to form over parts of interior and
southwest PR. Elsewhere and over the USVI mostly fair weather
skies with a slight chance for few showers in isolated spots.
The surface trough and low level pattern will gradually enhance
moisture convergence today through Thursday. This will bring an
increase moisture pooling and instability to the region. By late
Thursday and the for the remainder of the week, model guidance
suggest gradual improvement in the overall weather conditions
once again, as the mid to upper level inversion strengthens and
moisture transport diminishes across the region. So far model
guidance suggest somewhat drier conditions for the weekend with
only shallow trade wind induced convection, as high pressure will
continue to build aloft and north of the area increasing the
easterly trades.
&&
.AVIATION...In general, VFR conditions expected during the morning
hrs with just a few passing -SHRA affecting TJSJ/TIST/TISX/TNCM/
TKPK. Expect SHRA en route between the Atlantic waters and PR/USVI,
as the wind flow pushed them toward the islands. SHRA/+SHRA are
expected during the afternoon across the interior/west sections of
PR and MVFR celling are still possible at TJMZ and maybe in the VCNTY
of TJPS/TIST/TJSJ btwn 30/18z-22z. NE SFC winds at 5 to 10 knots
increasing at 10 to 15 knots with sea breeze variations aft
30/12z.
&&
.MARINE...Marine conditions will continue to deteriorate today
through at least thursday due to the moderate to fresh east to
northeast trade wind flow induced by the previously mentioned surface
high spreading eastward across the atlantic north of the region
and the trough/area of low pressure over the northern leewards.
Small Craft Advisories remains in effect and a High Risk Current
Risk is in effect for the northwest to north facing coastlines of
PR, Culebra and some beaches along the norther shore lines of the
northern USVI.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 76 88 75 / 50 30 30 20
STT 84 77 86 77 / 50 30 30 30

