Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service San Juan PR
305 PM AST Sat Oct 25 2014 upper levels...a northeast-Southwest Ridge over
Hispaniola will shift eastward over the local area Sunday and
Monday before a weak short wave trough passes through on Tuesday
followed by a weak northwesterly jet on Thursday. High pressure
returns Friday through Sunday.

At middle levels...low pressure in the Atlantic just east of Florida
will crowd the high pressure northeast of the area and the
associated ridge over the Dominican Republic...crossing weakly
over the area on Monday night with highs on either side. Very weak
gradients persist in The Saddle area through Friday. High pressure
extends into the eastern Caribbean from the southern central sub
Tropic Atlantic over next weekend. Weak moisture is observed at
middle levels through the period.

At lower levels...high pressure extends west southwest across the
local Atlantic waters through Sunday. Weak low pressure crosses
north of the area Monday and Monday night from the west. High
pressure leaves the Carolinas on Monday and transits east across
the western Atlantic until reaching the central Atlantic on
Friday. A tropical wave near 45 west will move west northwest and
develop a very weak low pressure over the Leeward Islands on
Wednesday...passing over or just north of the U.S. Virgin Islands
on Thursday and weakening over or just north of Puerto Rico
Thursday night. Better moisture follows through the first Tuesday
of November.


Discussion...some showers continued during the morning hours and
one shower left a few hundredths of an inch in the San Juan
Airport. But showers have diminished considerably during the middle
afternoon. Some showers...and possibly a thunderstorm...are still
expected to develop over the Cordillera Central and northwest
Puerto Rico during the late afternoon and extend into the evening
hours northwest of Aguadilla as southeast flow continues over the
area at lower levels. This pattern is expected to continue Sunday
and taper off Monday as the area becomes sandwiched between an
approaching tropical wave and a stalling cold front northwest of
Haiti. A weak tropical wave will pass through the Caribbean south
of the area Monday night followed by a continuation of drier weather
with only scattered showers in the west Tuesday and Wednesday.
Then a tropical wave with a very weak low pressure will approach
on Thursday sending better moisture over the area. Best chances
for rain should be on Thursday night or Friday according to
today's GFS solution. But the model shows the low embedded in the
wave weakening considerably as it moves over the area Thursday
night. Then...although a band of drier air passes over Friday
night...moisture returns in south to southeast flow and persists
through Tuesday of next week. Stronger features than the weak low
passage Thursday night are not foreseen in the next 10 days...but
temperatures during the next 10 days will average slightly above


Aviation...shra/tsra possible over the interior and northwestern PR
until 25/21z. Therefore...expect brief MVFR conds and mountain
obscurations in and around tjmz and tjbq. Also...vcsh at tjsj
possible. Low level winds from the east southeast around 10
kts...light and variable overnight.


Marine...although a weak northerly swell is expected tonight seas
will remain relatively tranquil and below 6 feet everywhere
through middle week. The low transiting the area Thursday and Friday
may generate some higher seas in the waters north of the area late
next week...but should have limited effect here.


Preliminary point temps/pops...
sju 78 91 77 89 / 20 20 20 20
stt 80 88 79 89 / 30 30 30 30


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



National Weather Service Glossary of Abbreviations