Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
257 PM AST Tuesday Sep 30 2014
Synopsis...mid-level ridge across the eastern Caribbean will
prevail through Wednesday....maintaining a fair weather pattern
across the region until Wednesday. A tropical wave is expected across
the local area on Thursday into Friday morning...increasing the
chances of showers and thunderstorms across the local islands.
After the tropical wave passes...much drier and stable airmass is
expected as a surface high moves in through the weekend.
Discussion...fairly warm day today with temperatures reaching 94
degrees so far in San Juan...tying the record set back in 2001. It
was also dry with only a few clouds observed...especially across
the northwestern portions of PR in the afternoon...otherwise
mostly sunny skies were observed. There is still a slight chance
of showers across northwest PR in the areas where clouds are
developing...but these are not expected to produce significant
accumulations if they develop. The rest of the local islands
should remain dry for the rest of the day.
Slightly more moisture is expected to move in for Wednesday and
instability increases slightly as well...so there is a better
chance for showers and isolated thunderstorms on Wednesday
afternoon across the northwest portions of PR. However the real increase
in moisture and instability is expected on Thursday as a tropical
wave moves into the local area. Scattered to numerous showers and
isolated thunderstorms are forecast with the passage of this wave
on Thursday into Friday. By late Friday night...much drier air is
expected to move into the local area and remain over the islands
through the weekend. Naaps model indicates that Saharan dust will
be moving in for Saturday along with a surface high pressure...so dry and
hazy conditions are very possible this weekend.
Behind the surface high pressure there are northeasterly winds and
more moist air...which may move into the local islands on Tuesday
after the high pressure passes. This may leave US with passing
showers and some clouds as the moisture increases.
Aviation...VFR conds will prevail at all taf sites and across the
local flying area during the prd. Low level winds will be mainly
from the east-southeast at 5-15 kts below fl150...becoming from NE-north above and increase to
20-25 kts near fl350. Few fair weather cumulus lines west/no sig vertical extent en
Route by the way east PR and Virgin Islands. No sig operational weather impacts
at this time.
Marine...seas are expected to remain at 3 to 4 feet for the next
few days with seas generally less than 17 knots.
Preliminary point temps/pops...
sju 78 92 78 91 / 20 20 30 30
stt 80 89 80 89 / 30 30 50 50