596
FXCA62 TJSJ 150838
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
438 AM AST Fri Nov 15 2024

.SYNOPSIS...
A cold front near the area will continue to produce showers across
the islands. Another frontal boundary is expected to reach the
islands on Saturday and Sunday, followed by drier conditions for
the first half of the next workweek. Marine and beach conditions
will be hazardous through early next week as a northerly swell
arrives.


&&

.SHORT TERM...Today through Sunday...

Overnight radar and satellite imagery indicated generally calm
conditions over land, with shower activity associated with a frontal
boundary focused over the Atlantic waters for most of the night.
Based on radar estimates, San Juan area and eastern Puerto Rico had
around 0.2 to 0.10 oh rain. Temperatures overnight ranged from the
mid to upper 70s along coastal and urban areas, and from the 60s to
low 70s across the mountainous regions. Light and variable winds
dominated the region.

The unstable and wet pattern will persist throughout the short-term
forecast. For today, light and variable winds ahead of the stalled
frontal boundary to the north will prevail across our region. This
boundary will maintain above-normal precipitable water values,
around 2 inches. Even most of the rain activity will stay over the
Atlantic waters, morning showers are expected to continue and move
inland, primarily over the northern coast of Puerto Rico, eastern
municipalities, and surrounding islands. Afternoon showers and
isolated thunderstorms, driven by diurnal and local effects, will
spread into the interior and coastal sectors later today.

Tonight, a change in the wind pattern is expected. Winds will shift
to a southerly component, driven by surface ridging over the
northeastern Atlantic. The current frontal boundary and its
associated moisture field are expected to be pushed to the north.
This will enhance showers Saturday morning across southwestern and
western Puerto Rico. Additionally, a polar trough over the Northeast
U.S. and its associated cold front will begin to move into the
western Atlantic waters.

By Saturday, strong high pressure building across the western
Atlantic will continue to push the cold front toward the Caribbean.
According to the latest model guidance, the front is expected to
cross our region by Saturday night into Sunday. Sufficient moisture
and instability will remain in place, making Sunday the most active
day of this period. After the front passes, a much drier air mass
will dominate the region, leading to a more stable weather pattern
starting Sunday night.

Overall, the flood threat will remain elevated through Sunday across
the islands with the risk to observe urban and small stream flooding
and quick river rises. The potential for mudslides and unstable
terrain will also persist due to continued saturated soil conditions
across much of the forecast area. Residents and visitors are
encouraged to continue monitor the forecast and any advisory or
warning for their area.

.LONG TERM...Monday through Friday...

After the cold front passes through the islands, a cooler and
drier air mass will filter into the region, with temperatures
dropping a little below normal. A mid to upper level ridge will
roll from the southeastern United States into the western
Caribbean. This feature will maintain a trade wind cap inversion
around 850 mb, with all the low level moisture trapped below this
level. During the first half of the workweek, the probability of
precipitation will be generally low, except just southeast of
Saint Croix, where the remnants of the cold front will linger.

As the high pressure system migrates toward the east and moves
into the central Atlantic, the winds will shift from the southeast
on Thursday and from the south on Friday. This will once again
pull moisture from the Caribbean into the local islands,
increasing the potential for some showers. Temperatures will
bounce back, and highs are expected to reach the upper 80s and low
90s once again, especially for the low-elevated and urban areas.


&&

.AVIATION...
(06Z TAFS)

VFR conditions across most of the TAF sites are expected to persist
through the next few hours. A cold front stalled to the north will
keep cloudiness, showers, and isolated thunderstorms this morning,
TJSJ and TIST having the best chance to observe rain. Afternoon
showers and isolated thunderstorms, driven by diurnal and local
effects, will spread into the interior and coastal sectors after
18Z. This could result in intermittent MVFR conditions and mountain
obscurations. Winds will remain generally with typical variations
and light, less than 10kt with the exception of any moderate to
heavy rain development. A more southerly component is expected to
develop tonight.

&&

.MARINE...
Gentle to moderate and variable winds will prevail over the next few
days. Marine conditions will become favorable for small craft
starting on Friday morning as moisture remnants along a cold frontal
boundary sink southward across the region. This will increase the
chance for showers and isolated thunderstorms across the regional
waters and passages. Pulses of a northerly swells are expected to
arrive and create hazardous seas today, stretching into the weekend.


&&

.BEACH FORECAST...
Pulses from a northerly swell will maintain a high rip current
risk for the beaches of northern Puerto Rico from Rincon to
Fajardo, Culebra, and Saint Thomas and St. John. This conditions
could deteriorate further tomorrow and Sunday, with higher
breaking waves anticipated.

Breaking waves will be lower in the beaches of the Caribbean Sea
in southern Puerto Rico, where the rip current risk is low.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Sunday night for PRZ001-005-
     008.

     High Rip Current Risk from this evening through late Sunday
     night for PRZ002-010-012.

VI...High Rip Current Risk from this evening through late Sunday
     night for VIZ001.

AM...Small Craft Advisory until midnight AST Saturday night for
     AMZ711.

     Small Craft Advisory from 6 PM this evening to midnight AST
     Saturday night for AMZ712-716.

&&

$$

SHORT TERM...YZR
LONG TERM....ERG