Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service San Juan PR
1040 PM AST Friday Mar 27 2015

Update...only passing isolated showers were observed across the
local area in the afternoon hours...then dissipating completely
and leaving mostly clear skies during the evening hours. Dry air
is expected to prevail over the local area overnight with
precipitable water values of around one inch...which is lower
than normal for this time of the year. Only a few clouds with
fair weather expected tonight. Very minor changes were made to the
temperature forecast for tomorrow as southeasterly winds caused
temperatures to rise to 88 degrees today across the San Juan
area...since the expected weather tomorrow is similar to what was
observed today the temperature forecast was adjusted to 88 degrees
for persistence. Other than that no changes were made or seemed
necessary at the moment.


Aviation...VFR conds expected at all taf sites through the forecast
period. Brief MVFR conds will remain possible from 28/18z to
28/22z in and around tjbq/tjmz and in tncm and tkpk. Surface winds until
28/12z east up to 10 knots...after 28/12z east 10-20 knots gusting to 28
knots with sea breeze variances. East southeast winds up to 25 knots
between fl010 and fl090.


Marine...very borderline small craft event possible as seas
almost reached 7 feet at The Rincon buoy. Latest guidance had a
small area with 7 foot seas across the offshore Atlantic
waters...however after much analysis and consideration...we
decided to keep the seas at a maximum of 6 feet. Winds will be up to
20 knots into Saturday and seas up to 6 feet tonight and into
Saturday across most of the local waters. Small craft should
exercise caution.


Previous discussion... /issued 255 PM AST Friday Mar 27 2015/

Synopsis...upper level ridge will hold through Sat then weaken
somewhat next week as broad trough becomes dominant weather feature
across the Atlantic. Ridge will then weaken more rapidly next weekend.

Discussion...dry weather will prevail through the weekend beneath
strong upper level ridge. Ridge and associated subsidence
inversion begin to weaken early-middle next week promoting moisture
transport and enhancing middle-level instability mainly Tuesday and Wednesday
with T-storms possible. Some drying expected Wednesday night into Thursday.
A sharp trough will move across the area next weekend.

Aviation...VFR conds expected at all taf sites through the forecast
period. Brief MVFR conds will remain possible through 27/22z in
and around jbq/jmz. Southeast winds 15 to 20 knots through 27/22z becoming
light and variable overnight.

Marine...winds and seas will subside tonight into Monday. Winds
and seas build again next week.


Preliminary point temps/pops...
sju 76 88 75 88 / 0 0 10 10
stt 76 85 74 85 / 0 0 10 10


Sju watches/warnings/advisories...
Coastal waters...none.



National Weather Service Glossary of Abbreviations