678
FXCA62 TJSJ 280855
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Sun Apr 28 2024

.SYNOPSIS...A surface high pressure over the western Atlantic will
promote northeasterly winds through at least Wednesday. Breezy
conditions are possible during the start of the workweek. Drier
air between a surface low over the north central Atlantic and the
surface high should reach the local area under the northeasterly
fetch. However, moisture content should remain at normal levels.
By mid-week onwards, instability and moisture levels increase
once again as an upper level trough lingers over the western
Atlantic and lighter east to southeast winds return. Life-threatening
rip currents are expected during the first part of the week.


&&

.SHORT TERM...Today through Tuesday...

Calm weather conditions prevailed across Puerto Rico and the U.S.
Virgin Islands, with quick passing showers over the local waters.
Low temperatures were observed in the range from the mid to upper
60s across the higher mountains and valleys, and from the low to mid
70s along the coastal areas. Breezy conditions prevailed across the
islands under a northeasterly wind flow.

Today, we expect mostly tranquil weather conditions during the
morning hours, with passing showers moving into the eastern coast of
Puerto Rico and the U.S. Virgin Islands at times. During the
afternoon hours, rainfall development is likely over portions of the
interior and southwest Puerto Rico due to lingering moisture of a
trough/frontal boundary in combination with daytime heating and local
effects. Precipitable water content values are in the range between
1.45 to 1.60 inches. Showers and isolated thunderstorms across the
mentioned sectors may result in flooding, river rises, mudslides and
isolated flash flooding. Soils are very saturated due to the rains
from the previous weeks, and any additional accumulations could
result hazardous. We continue to encourage citizens of Puerto Rico
and visitors to closely watch the weather conditions during the next
several days due to the potential for showers and thunderstorms each
afternoon.

A gradual improvement on weather conditions is anticipated over the
next few days, as a strong surface high pressure moves offshore the
eastern coast of the U.S. towards the Central Atlantic. This feature
will promote the entrance of a slightly drier airmass into the
region. Nonetheless, precipitable water content values should remain
within normal seasonal values. In response to the surface high,
moderate to fresh northeasterly winds will prevail today through at
least Tuesday. Then, shifting from the east on Wednesday. Despite of
some drier air across the region, shower development is anticipated
every afternoon across portions of the interior and southwestern
portions of Puerto Rico. However, rainfall accumulations should be
less compared to the previous days. High temperatures will remain in
the mid to upper 80s along the coastal and urban areas, and in the
mid to upper 70s along the mountains and valleys.

.LONG TERM...Wednesday through Sunday...

A more unstable and wetter pattern is expected to evolve during
the long term period as a mid-to upper-level trough develops and
remains nearly stationary over the west/southwestern Atlantic. By
Wednesday, the surface high pressure north of the area is
expected to weaken and in response winds are expected to veer from
the southeast, and become lighter through the rest of the period.
Meanwhile, old frontal boundaries and a restrengthening of the
surface low over the north central Atlantic will induce weak
troughs or perturbations across the northeastern Caribbean through
the end of the workweek. Steering winds will acquire a westerly
component and convective development with heavy showers are
possible over portions of the eastern interior, San Juan and
vicinity and over the USVI, particularly on Thursday and Friday.

Having said that and based on the latest guidance, all afternoons
through the long term period should be active with possible
flooding impacts and mudslides in areas of steep terrain across
Puerto Rico. For the USVI, an increase in the frequency of
showers and isolated thunderstorms is possible from Thursday
onwards. Heat indices across the lower elevations of the islands
could likely range between 102-106 degrees on Friday and Saturday
before the onset of afternoon convection.



&&

.AVIATION...

(06z) TAFS

Expect mainly VFR conditions expected to prevail across all terminals
through the forecast period. An increase in TSRA/SHRA this aftn may
produce brief MVFR cigs across TJPS aft 28/17Z. VCSH expected for
the TJSJ//TIST/TISX terminals after 28/13Z. Mountain obsc is
expected for the Cordillera Central from 28/13-22z. Breezy conds are
expected with winds out of the NE at 12-16 kts, and stronger gusts
after 28/13-14Z.


&&

.MARINE...

Light to moderate northeast winds will prevail today across the
regional waters, locally higher winds are expected due to sea
breeze variations across coastal areas. Winds are expected to
incrs from moderate to fresh tonight and continue through at
least late Tuesday as a surface high pressure moves off the US
East Coast. These increasing winds and a northerly swell spreading
across the local waters on Monday will further deteriorate seas
through at least mid-week. Small Craft Advisories are in effect
for the Atlantic waters and the Mona Passage.


&&

.BEACH FORECAST...

Short-period waves and onshore flow along the northern and
eastern beaches of the islands will promote a moderate risk of rip
currents today. A northerly swell arriving on Monday and stronger
winds will increase the risk of rip currents and promote life-
threatening rip currents from Monday through at least late
Wednesday. For more information and details about the latest
forecast please refer to the Surf Zone Forecast (SRFSJU).


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from 6 PM this evening to 6 AM AST
     Wednesday for AMZ711.

     Small Craft Advisory from noon Monday to midnight AST Tuesday
     night for AMZ712-741.

&&

$$

AVIATION/SHORT TERM...GRS
MARINE/LONG TERM....13