Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 081518

Area Forecast Discussion
National Weather Service San Juan PR
1118 AM AST Wed Apr 8 2020


Widespread showers have continued this morning, with significant
rainfall observed in the metro area having caused local flooding.
This is associated with moisture convergence over the region due
to the remnants of a frontal boundary traversing the area. The
SJU 12Z upper air sounding observed precipitable water levels to
be at 1.92 inches. The showers have subsided over the island for
now during the last couple of hours. However, a resurgence in
shower activity is expected this afternoon; sufficient moisture
persists to help aid in the development of showers due to local
and diurnal effects. The peak in shower activity is expected to be
interior Puerto Rico, stretching to northern Puerto Rico, and
there is a moderate risk of flooding from these showers.



BKN/OVC skies with CIGS at around FL060 expected across
most of the local terminals today. SHRA over the local area will
cause VCSH across most of the local terminals with TEMPO MVFR
possible as the SHRA affects the terminals. TJSJ, TJMZ, and TJBQ
could observe TEMPO MVFR conds this afternoon, while TIST can
observe MVFR conds late this afternoon in the the evening. Winds
from the SE to NE at 10-15 knots through 08/23Z, becoming lighter



Gentle to moderate winds continue out of the east, veering more
southeasterly during the day today. Showers also continue,
especially across the Atlantic waters and local passages. Seas are
gradually subsiding; wave heights up to 6 feet are possible in the
Mona Passage, but elsewhere, seas are expected to remain around 5
feet or less. Furthermore, there remains a high risk of rip
currents at beaches along the northwest to northeast coasts of
Puerto Rico as well as Culebra.


.PREV DISCUSSION... /issued 453 AM AST Wed Apr 8 2020/

Moisture associated with a weak frontal boundary continue across
the area. This will result in passing showers across the area
in the morning hours specially across northern and eastern
sections of Puerto Rico. Them in the afternoon hours, scattered
to numerous showers will affect the interior and northwestern
sections of Puerto Rico. Urban and small stream flooding still
possibles with the heaviest showers. Drier weather is anticipated
for Friday and continue for the rest of the weekend. Across the
regional waters, seas up to 6 feet across the Atlantic waters,
therefore small craft operators should exercise caution.

SHORT TERM...Today through Friday...

Abundant low-level moisture associated with an old frontal boundary
continues situated over the area. This has resulted in scattered to
numerous showers across the northern and eastern portions of Puerto
Rico during the overnight hours. Showers will continue to affect
these areas through the morning hours. Then, during the afternoon
hours, as the available moisture combines with diurnal heating and
sea breeze convergence, scattered to numerous showers are expected
across portions of interior, western, and the northern half of
Puerto Rico. Once again, the low-level flow remains very light and
thus, slow-moving showers are expected. Therefore, the potential is
there for urban and small stream flooding to materialize in areas in
areas that a prolonged period of heavy rainfall activity. Across the
USVI, scattered showers are expected from time to time, especially
across Saint Thomas and Saint John. The activity across these areas
may result in ponding of water on roadways and in poor-drainage

Weather conditions are expected to improve for both Thursday and
Friday as the old frontal boundary and its associated moisture lifts
to the northeast and drier air moves over the area under a southerly
flow. Therefore, more limited shower activity is expected. However,
some afternoon showers are still expected to develop across interior
and northern portions of Puerto Rico due to local and diurnal
effects. Due to the southerly flow, high temperatures along the
urbanized areas of northern Puerto Rico may top out in the lower 90s
both days

LONG TERM...Saturday through Thursday...

On Saturday, a drier mas mass is expected to move across the
region limiting the afternoon convection. However, some passing
showers could develop across across western and interior sectors
of Puerto Rico. These southeasterly wind flow is expected to
result in warmer temperatures across the coastal areas of northern
Puerto Rico. On Monday, the wind flow change from east to
northeast pushing fragments of low-level moisture across the
region. . Afternoon development should be focused over the
interior and western sections of Puerto Rico.

On Tuesday to Wednesday, a building high pressure located in the
northeastern Atlantic will carry some low-level moisture across
the region. This moisture in combination with the local effects
can result in more shower activity across the main island,
especially in the afternoon hours due to the diurnal heating. For
the U.S. Virgin Islands, some passing showers still possible in
the morning hours. For Thursday, GFS model guidance suggest
a little less moisture across the region, that said, less chance
of shower activity could be possible.

Sct SHRA expected across eastern PR and the northern
USVI through at least 08/14z, resulting in VCSH mainly across
TJSJ/TIST. SHRA expected across interior and northern PR as well as
across the northern USVI from 07/16z through 08/23Z. This will
result in VCSH across TJMZ/TJBQ/TJSJ/TIST. MVFR conditions will be
possible if SHRA affect the terminal sites. Winds will be from the E-
ENE below 10 kts through 08/12z, increasing to 12 to 18 kts with sea
breeze variations after 08/14z.

Across the regional waters, seas between 4 to 6 feet across the
Atlantic waters. Therefore, small craft operators should
exercise caution especially over the Atlantic waters and Mona
passage. Over the Caribbean waters, seas between 2 to 5 feet are
expected. A slowly weakening frontal boundary will aid in
maintaining showers mainly across portions of the nearshore
Atlantic waters and local passages.

expected to
continue for the next few days with winds up to 10 knots or less.
There is a moderate risk of rip currents at north- facing beaches,
with generally low risk elsewhere.


SJU  85  76  90  76 /  50  50  40  20
STT  86  76  84  77 /  50  40  20  10


PR...High Rip Current Risk until 6 PM AST this evening for Culebra-
     North Central-Northeast-Northwest-San Juan and Vicinity-



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