Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxca62 tjsj 160929 
afdsju

Area forecast discussion
National Weather Service San Juan PR
529 am AST Sat Dec 16 2017

Synopsis...
under a ridge pattern aloft, another fair weather day is expected
across the islands. A surface high pressure across the central
Atlantic will tighten the local pressure gradient increasing the
northeasterly wind flow through the weekend.

&&

Short term...tonight through Monday...
a persistent mid to upper level ridge will suppress wide spread
convection across Puerto Rico and the U.S. Virgin Islands through
the beginning of next week. San Juan skew-T soundings shows drier
air from 800 mb to 200 mb this is also a reason why showers will
be limited across the region through Wednesday. Similar to the
previous days fair weather conditions will remain across the
forecast area with the possibility for a occasional shower during
the afternoon. Otherwise mostly sunny skies with daytime high
temperatures reaching the low to mid 80s with an easterly wind of
10 to 15 mph with higher gusts possible.

Long term...Tuesday through Saturday...
the ridge pattern aloft will hold across the islands through the
upcoming mid-week. Therefore, expect mostly mostly clear skies
with a few passing showers from time to time each day. The ridge
pattern is forecast to slowly erodes during the latter part of
next week, as a polar trough amplified from the northeast into the
northeastern Caribbean. There is enough uncertainty about the
final solutions at this time. However, if weather guidance are in
the right track, this will result in a better chance for shower
activity across the local islands, as well as thunderstorm
development.

&&

Aviation...
VFR conditions are expected to prevail for the reminder
of the taf period. This morning sfc winds 10 to 15 kts before
increasing to 15 to 20 kts with higher gusts by 16/14z. Isolated
showers are possible during the afternoon but any showers that might
form will be short-lived.

&&

Marine...
a northerly swell will continue to slowly erodes across the
Atlantic waters through the morning hours. Mariners can expect
seas between 5 and 7 feet across the Atlantic offshore waters.
Elsewhere, seas between 4 and 6 feet. Winds will blow from the
east to east-northeast at 10 to 20 knots. A Small Craft Advisory
is in effect across the Atlantic waters until at least 11 am AST
today. However, rough and hazardous seas will return across the
offshore waters and Caribbean waters later tonight.

For the beach goers, there is a high risk of rip currents along
the north facing beaches of Puerto Rico and Culebra and along the
north facing beaches of Saint Thomas and Saint John.

&&

Preliminary point temps/pops...
sju 84 77 84 77 / 10 20 30 30
stt 86 76 87 76 / 20 20 30 30

&&

Sju watches/warnings/advisories...
PR...high rip current risk through this afternoon for Culebra-north
Central-Northeast-northwest-San Juan and vicinity-southeast-
western interior.

Vi...high rip current risk through this afternoon for St...
John...and adjacent islands.

Am...high rip current risk through this afternoon for coastal waters
of northern USVI and Culebra out 10 nm-coastal waters of
southern USVI Vieques and eastern Puerto Rico out 10 nm.

Small Craft Advisory from 2 am Sunday to 7 am AST Monday for
Anegada Passage southward to 17n-Atlantic waters of Puerto
Rico and USVI from 10 nm to 19.5n-Caribbean waters of
Puerto Rico from 10 nm to 17n-Mona Passage southward to 17n.

Small Craft Advisory until 11 am AST this morning for Atlantic
waters of Puerto Rico and USVI from 10 nm to 19.5n.

&&

National Weather Service Glossary of Abbreviations