textproduct: San Juan

KEY MESSAGES

Issued at 411 AM AST Sun Dec 21 2025

* A fading northeasterly long period swell will continue to result in deteriorated marine and coastal conditions today and tonight. Another stronger northerly swell will again deteriorate marine and coastal conditions Tuesday through at least the rest of the workweek.

* A High Risk of Rip Currents continues for the northern exposed beaches of Puerto Rico and Culebra, as well as eastern St. Croix, through 6 AM AST Monday. These conditions then return by around late Tuesday.

* A Small Craft Advisory continues for the Atlantic waters and the Anegada Passage until at least midnight tonight. These conditions then return by around Tuesday.

* Light to moderate passing showers under northeasterly winds will continue across windward sectors of PR and the USVI today, afternoon showers then forecast for interior to SW PR.

* For the Christmas Eve into Christmas Day, a wet and unstable weather pattern is forecast with a moderate to high chance of widespread showers and thunderstorms. Residents and visitors of Puerto Rico and the US Virgin Islands are urged to stay tuned for further updates in the forecast.

Short Term(Today through Tuesday)

Issued at 411 AM AST Sun Dec 21 2025

Current satellite derived Precipitable Water (PWAT) imagery indicate patches of moisture with up to 1.60 in, steered by northeasterly flow, moving mainly around St. Croix. Other coastal areas currently have PWAT values of around 1.30 to 1.40 in. Light to moderate passing showers over the local waters have continued, moving into coastal windward areas. SInce midnight, radar estimated accumulations over eastern Puerto Rico have resulted in up to isolated amounts of around 0.40 in. Radar estimated accumulations were also detected over Culebra, Vieques, the USVI, north-central PR and southeastern PR. Patchy fog was also observed over areas of the interior. Minimum temperatures were in the upper 50s to low 60s across higher elevations of PR, in the upper 60s and mid 70s across lower elevations of PR, and in the low to mid 70s across the USVI.

A series of surface highs and frontal lows over the Atlantic will result in northeasterly steering flow through most of the period. This will bring in patches of moisture and passing showers embedded in the trade winds towards windward sectors, resulting in generally seasonal PWAT values. This available moisture will mostly be confined to the lower levels, as a mid to upper level ridge continues over the region to start the week. This ridge will continue to provide stability and limit vertical shower development. 500 mb temperatures will be warmer than normal, but will gradually decrease as the period progresses. The ridge will gradually weaken as the short term period progresses as a polar trough moves over the western Atlantic late tonight and continues moving east as the period progresses. 500 mb temperatures will be colder than normal by Tuesday. Patches of moisture and passing showers with generally minor accumulations will continue to be steered over windward areas of the islands during the period, mainly during the morning and overnight hours. Limited afternoon convection is also forecast each day for mainly west/southwest PR due to sea breeze convergence and diurnal hearing. Heavier showers can result in ponding of water over roadways and poorly drained areas. 925 mb temperatures will be at seasonal values but with a slight cooling trend as the period progresses. Maximum temperatures will be in the mid to upper 80s across lower elevations of the islands, with isolated/urban areas a bit higher. Minimum temperatures will remain similar to tonight, with patchy fog also developing over areas of the interior during the overnight hours.

Long Term(Wednesday through Sunday)

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

(06Z TAFS) Issued at 411 AM AST Sun Dec 21 2025

Mainly VFR conditions across the terminals. Passing -SHRA at or in the VCTY of TJBQ/TJSJ/TIST/TISX with, between 21/17 - 23Z, -SHRA /SHRA developing over interior to WSW PR that can also reach the VCTY of TJPS/TJBQ. Winds from the NE after 21/13Z up to 15 to 19 kts, with higher gusts and sea breeze variations.

MARINE

Issued at 411 AM AST Sun Dec 21 2025

The moderate to locally fresh east to northeast winds will continue for the next few days. These winds along with pulses of a fading long- period northerly to northeasterly swell will promote hazardous seas for small craft, particularly across the Atlantic waters and Anegada passage. Small Craft Advisories remain in effect due to seas gradually building up to 8 feet through this evening. Marine conditions will briefly improve tonight into Monday, before another stronger northerly swell promotes hazardous marine conditions for small craft by late Tuesday into midweek.

BEACH FORECAST

Issued at 411 AM AST Sun Dec 21 2025

For the rest of the day, a moderate risk of rip currents will persist as coastal marine conditions deteriorate with the arrival of the north-northeasterly swell. Therefore, from 6 PM AST onward, there is a high risk of rip currents across all northern coastal areas, including Culebra and St. Croix, until Monday evening. 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 AMZ711-723.

Small Craft Advisory until midnight AST tonight for AMZ712-716.