Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 312009

Area Forecast Discussion
National Weather Service San Juan PR
409 PM AST Tue Mar 31 2020

Mainly fair weather conditions prevailed across the islands during
the morning and early afternoon hours. These weather pattern is
expected to continue for the rest of the day and for tomorrow.
However, some cloudiness and passing showers can develop over
southwestern sections of Puerto Rico due to the local effects and
diurnal heat. East to northeast winds are prevailing between
15-20 mph.


.SHORT TERM...Today through Thursday...

Overall fair weather conditions are expected to continue through the
short term period as a weak surface high dominates the region
through at least Wednesday. As the high moves further east into the
central Atlantic, winds are expected to shift from the southeast
through at least Thursday, generating warmer temperatures across the
area, with highs in the upper 80s to low 90s across the northern and
eastern half of Puerto Rico. Across the U.S. Virgin Islands max
temps should range in the mid to upper 80s.

At upper levels a ridge will hold through Wednesday, maintaining
fairly stable conditions and drier air aloft. This will inhibit the
vertical development of showers across the islands and diurnal
activity will be focus over portions of the interior, northern and
western PR. However, minor rainfall accumulations are expected with
this activity through at least Wednesday. On Thursday, a deep
layered lighter southerly wind flow and a 500 mb trough will move
aloft. This will increase the potential for better rainfall amounts
across the islands.

.LONG TERM...Friday through Wednesday...

.PREV DISCUSSION... /issued 509 AM AST Tue Mar 31 2020/

On Friday and into the weekend, the combination of the approaching
frontal boundary along with the proximity of the upper level trough
and a fairly light southerly flow, will result in increasing instability
aloft and low level moisture convergence. The slightly warmer than
normal high temperatures is also forecast to continue for the north
coastal areas at least until Friday.

Moisture pooling will return over the weekend as the frontal boundary
and associated shear line is forecast to stall and drift southwards
across the northeastern Caribbean by Sunday. This along with the
proximity of the upper level trough will increase the potential
for shower development across the islands and coastal waters each
day. Some of the shower activity will be enhanced and therefore
urban and small stream flooding will be possible in isolated areas
over the weekend and into early next week. Under this expected
moist and unstable airmass, and based on latest model guidance,
the best potential for convective development will be on Saturday
and continuing through Sunday. Improving conditions is expected
on Monday as the wind flow will shift once again and become more
northerly. This is in response to a surface high pressure ridge
which will build and spread across the west Atlantic. This will
however be short-lived as low level moisture from the frontal
remnants will return and be lifted back across the area Tuesday
through Wednesday. Therefore this fairly moist and unstable
pattern during the period should result in potential for early
morning and afternoon shower development in and around the islands
each day.



Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. VCSH are possible this afternoon
for TJMZ/TJBQ, and no lightning is expected. Winds primarily out of
the east at 10-15 knots with sea breeze modifications, and turning
more from the ESE by tomorrow morning for TIST/TISX/TNCM/TKPK.



Seas are expected to continue at less than 4 feet
across the regional waters through at least late Friday. East
winds today should remain at 15 knots or less, becoming more light
and southerly on Wednesday. A long period northerly swell is
expected to move across the local waters later in the weekend.


The RH dropped to 50% around noon today at Camp Santiago. Winds
peaked at 14 mph from the southeast with gusts up to 21 mph. The
KDBI was at 580 from yesterday observation. A fire danger
statement continues in effect for the southeast coastal plains of
Puerto Rico through late this afternoon.


SJU  72  88  74  89 /   0  10  10  10
STT  73  84  74  84 /  10  20  20  20




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