Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service San Juan PR
1132 am AST Sat may 23 2015

Update...hazy skies have prevailed across the forecast area so
far today. early morning streamers developed off the
USVI...Vieques and Culebra. This created some showers between the
northern USVI and eastern PR. Also...showers were streaming off El
Yunque westward reaching Vega Alberta by 11 am AST. For the rest of
the day...isolated showers will continue streaming off El Yunque
affecting parts of the San Juan metropolitan area and scattered showers
are expected to develop mainly over western PR during the
afternoon. No changes so far to previous forecast.


Aviation...VFR conds overall across all terminals.
However...isl/sct rain showers is forecast over the interior and western
PR this afternoon...this can create brief periods of MVFR conds
impacting mainly jmz. The 23/12z tjsj upper air sounding indicated
low level easterlies at 10-19 knots.


Marine...buoys across the nearshore waters of PR and the USVI are
indicating seas of 3-4 feet and east winds at 15 knots with higher


Previous discussion... /issued 548 am AST Sat may 23 2015/

Synopsis...upper level low south of Bermuda is pressing against
the subequatorial ridge over northern South America maintaining the
subtropical jet over Puerto Rico. At mid-level...a weak ridge is
dominating the eastern Caribbean. Surface high pressure will exit
the eastern US tonight and build over the western Atlantic on
Sunday...then will be absorbed by a broad high pressure over the
eastern Atlantic on Monday. Dry and stable air mass with Saharan
dust particles will prevail across the local area trough early
next week creating hazy skies. Wetter pattern possible by the end
of the month.

Discussion...satellite loops continue to show high clouds moving
westward across the local region. Radar detected very small showers
across the regional waters early this morning. No measurable rain
was observed over the islands overnight. For the rest of the Memorial
weekend...continue to expect dry and stable conditions dominating
the local islands. A strong subsidence inversion between 850mb-700mb
associated with the Saharan air layer will keep the chances of showers
fairly low through Sunday. Suspended Saharan dust particles will create
hazy skies and areas of reduced visibilities. Hi-res model guidance
only suggest a shower or two in isolated spots of west Puerto Rico
this afternoon.

For early next week...wetter trade winds will bring scattered
passing showers to the windward side of the islands...followed by
some shower development over the interior and west PR each afternoon.
By the end of may...operational models are suggesting deep moisture
advecting over PR/USVI in response to an area of low pressure
developing near Bahamas.

Aviation...VFR likely through sun. Tist/tisx are apparently having
false ceilings due to Saharan dust WI impvg conds expeceted on sun. Scattered
rain showers/thunderstorms and rain western PR Sat/sun but slim chance MVFR. Wind below fl100 east 12-
20 knots increase 15-25 today then 12-20 again on sun.

Marine...local and regional buoys are reporting seas of 4 feet
or less with winds around 15 knots. Winds and seas will remain
below Small Craft Advisory criteria for all waters through the end
of the month.


Preliminary point temps/pops...
sju 89 78 88 77 / 20 20 20 40
stt 88 78 88 78 / 20 20 20 40


Sju watches/warnings/advisories...



National Weather Service Glossary of Abbreviations