National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXCA62 TJSJ 202027
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
427 PM AST Sat Apr 20 2024

.SYNOPSIS...

A gradual improvement in weather conditions is expected this
afternoon after the shower activity ends across the southern and
eastern portions of Puerto Rico. However, an unstable weather
pattern is expected to return by the beginning of the next
workweek with the potential of heavy showers and isolated
thunderstorms across the islands.

&&

.SHORT TERM...Tonight through Monday...

Mainly fair weather conditions have prevailed across much of the
region today. However, showers were seen over the eastern and
southern portions of Puerto Rico and the local waters during the
afternoon hours. Doppler radar estimated rainfall accumulations
between 1.0 to 1.5 inches of rain across these areas. Line of
showers were observed streaming off the U.S. Virgin Islands, with
minimal accumulations over Vieques. The Luis Munoz Marin Int.
Airport in San Juan observed 86 degrees Fahrenheit. The coastal
and urban areas temperatures stayed in the mid to upper 80s, and
from the low to mid 80s at the higher elevations.

The shower activity across the southern slopes of Puerto Rico will
gradually finish before sunset, and mainly fair weather conditions
will be observed during the overnight hours. However, passing
showers cannot be ruled out across portions of eastern Puerto Rico,
including Vieques and Culebra. On Sunday, generally calm
conditions are anticipated with shower activity developing over
portions of western Puerto Rico due to daytime heating and local
effects. Therefore, there is the potential for ponding of water
and minor flooding in low drainage areas. From Sunday night into
Monday, moisture associated with the trough that affected early
this week will combine with another approaching surface trough,
increasing the potential for showers and isolated thunderstorms
across the area. In terms of the timing, the U.S. Virgin Islands
and eastern Puerto Rico will experience showers during the early
morning hours. Then, followed by afternoon convective activity
across the interior and western Puerto Rico. This event will
increase, once again, the potential for flooding, river rises and
mudslides. Winds are expected to veer from the southeast by
Monday. Warm to hot temperatures are expected with heat indices
reaching the 100s across portions of northern Puerto Rico.

.LONG TERM...Tuesday through Saturday...

.PREV DISCUSSION.../Issued 451 AM AST Apr 20 2024/

A wet and unstable weather pattern is expected to return in the long-
term forecast. A surface high pressure across the central Atlantic
and a surface low over the western Atlantic will induce east-
southeast winds across the CWA. Consequently, this wind pattern will
promote warmer temperatures over the islands and pull tropical
moisture into the area. Precipitable water content is expected to
remain within the range of 1.9 to 2.2 inches. These values exceed
the 90th and 99th percentiles of the climatological normal,
indicating well above-normal moisture levels for this time of year.

In terms of instability, an upper-level trough is expected to deepen
throughout the week, inducing an inverted surface trough west of
Puerto Rico. These features will gradually progress eastward during
the week, sustaining unstable weather conditions capable of
generating deep convective activity. The likelihood of convective
activity will be highest during afternoon hours as high moisture
content and instability combine with surface heating and local
effects.

Soils are expected to remain somewhat saturated by Tuesday due to
rains from previous days, with rivers still experiencing elevated
streamflows. Consequently, the flood risk will remain elevated to
significant through at least Friday, particularly during afternoon
hours. Quick river rises, river flooding, and landslides are also
possible, primarily across Puerto Rico. In the US Virgin Islands,
minor flooding with brief periods of excessive runoff is possible
each day of the week.

&&

.AVIATION...
(18z) TAFS

Mainly VFR conditions are expected at all TAF sites. However, VCTS
will remain possible at JPS through about 20/23z. SHRA will stream
across the Atlantic waters and passages, occasionally reaching the
USVI terminals overnight. Winds are from the NE at 5-12 kts,
becoming at 10 knots or less overnight.

&&

.MARINE...

Gentle to moderate northeasterly wind flow will continue to prevail
across the local waters through at least early the next workweek,
becoming light to gentle from the east southeast on Tuesday. A small
northeasterly swell will move across the Atlantic waters through the
weekend. However, seas will remain less than 5 feet for the most
part.

&&

.BEACH FORECAST...

There is a moderate risk of life- threatening rip currents along
the north-facing beaches of the local islands. Please remember to
heed the advice of the local beach patrol and flag warning
systems.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...CAM
LONG TERM....GRS
PUBLIC DESK...RVT