textproduct: San Juan

KEY MESSAGES

Issued at 159 PM AST Sun Dec 21 2025

* Cloudiness and passing showers are forecast for the rest of the day into the night hours across the northern and eastern sections of Puerto Rico.

* Some hazardous marine and coastal conditions will persist as the diminishing north-northeasterly swell continues to weaken across the local waters.

* For the upcoming week, showers are forecast to increase due to moisture from a frontal boundary and an upper-trough. Residents can expect frequent light to moderate showers along the north coast.

* A cold trend is forecast to start just Wednesday, as winds turn from the north-northeast and drier air filters in.

Short Term(This evening through Tuesday)

Issued at 159 PM AST Sun Dec 21 2025

Sunny to partly cloudy skies were observed across Puerto Rico and the U.S. Virgin Islands today. Streamers developed downwind of the USVI around noon, while low-level cumulus clouds were developing over the mountain ranges of PR. This surge in low-level moisture will combine with daytime heating and the sea breeze convergence to produce showers mainly over west/southwest PR. Breezy conditions should continue across most coastal areas with gusts between 25-30 mph. Maximum temperatures were in the mid 80s along the northern coastal areas and in the upper 80s to low 90s across the southern areas.

For tonight, a weak induced surface trough will increase showers across the USVI and eastern half of PR. This activity may lead to ponding of water in roads and other poor drainage areas. Similar conditions are expected on Monday and Tuesday, with sunny to partly cloudy skies prevailing during the day, and showers developing in the afternoons over west/southwest PR, followed by passing showers during the night across the USVI and windward areas of PR. However, moisture content is expected to recover to around above normal levels briefly on Tuesday afternoon due to an approaching front from the Atlantic waters. Meanwhile, an upper level trough will bring colder than normal 500 mb temperatures late in the period and through midweek. This could lead to stronger showers and possible isolated thunderstorms.

Long Term(Wednesday through next Saturday)

Issued at 411 AM AST Sun Dec 21 2025

The previous forecast remains on track, with Christmas Eve into Christmas Day expected to be the most active and potentially unstable period of the long-term forecast. Latest model guidance continues to indicate mid-level temperatures cooling to below- normal values, particularly around -10 to -11 degrees Celsius, which would support somewhat higher instability. This pattern will be associated with a polar trough extending southward into the Caribbean, while an additional upper-level trough interacts with a surface frontal boundary north of the region. This boundary is forecast to move close to the area or possibly cross the region, promoting an increase in moisture along with enhanced upper-level divergence.

Even so, precipitable water (PWAT) values remain near typical levels for late December, generally around 1.5 to 1.6 inches, or near the 50th percentile/seasonal normal. With moisture trending closer to seasonal values, rain chances have been adjusted slightly downward. Expect a moderate chance (around 50 to 60 percent) for scattered showers with isolated thunderstorms. At this time, forecast instability appears limited, favoring mainly shallow convection with only a few thunderstorms. Overall, model solutions have been fairly consistent from run to run regarding the approach of these features. However, uncertainty remains regarding the exact impacts across Puerto Rico and the U.S. Virgin Islands.

A gradual improvement in weather conditions is expected late in the workweek into the weekend, as drier-than-normal air and a more stable pattern become established, leading to generally quieter conditions. Cooler temperatures are expected to persist through the holiday weekend, supported by a trend toward below-normal 925 mb temperatures. Any rainfall should be limited, with only low-end shower chances possible if brief patches of moisture move through.

AVIATION

(18Z TAFS) Issued at 159 PM AST Sun Dec 21 2025

Mainly VFR conditions are expected across all terminals during the next 24 hours. However, quick passing -SHRA could move at times across TJSJ and the USVI terminals. Brief MVFR conds are possible with these trade wind showers. The 21/12z TJSJ sounding indicated NE winds up to 18 kt blo FL050.

MARINE

Issued at 159 PM AST Sun Dec 21 2025

No changes to previous forecasts. Deteriorated marine conditions persist for the rest of the afternoon hours into the early evening hours due to a north-northeast swell fading in the local waters. The latest buoy data from the offshore waters shows seas remain up to 7 feet. Given the conditions, the small craft advisory is still in effect for the offshore Atlantic waters and the Anegada passage until 12 AM AST on Monday. For the rest of the local waters and seas, waves will remain up to 5 feet. Improving marine conditions are forecast for Monday morning, just a break until late Wednesday when another northerly swell moves into the area, deteriorating marine conditions again for small craft operators.

BEACH FORECAST

Issued at 159 PM AST Sun Dec 21 2025

The fading north-easterly swell will continue to result in a high risk of rip currents across all northern coastal areas, including Culebra and St. Croix, until late tonight. Coastal conditions will improve by Tuesday; however, another northerly swell will increase the risk up to high again by late Wednesday into Thursday.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through late tonight for PRZ001-002-005- 008-012.

VI...High Rip Current Risk through late tonight for VIZ002.

AM...Small Craft Advisory until midnight AST tonight for AMZ711-712- 716-723.