textproduct: San Juan

KEY MESSAGES

Issued at 500 AM AST Thu Dec 18 2025

* A subsiding northerly swell will continue to produce hazardous marine and beach conditions today. The High Surf Advisory remains in effect along northern Puerto Rico and Culebra until this afternoon, while the High Risk of Rip Currents remains in effect until early Friday.

* Marine and beach conditions are forecast to deteriorate again from Saturday afternoon into Sunday due to strengthening winds and another northerly swell.

* Mostly fair weather conditions during the morning across PR and the USVI, then an approaching perturbation is expected to bring a moderate chance of showers across the interior and western PR this afternoon.

* Cooler temperatures and better rain chances are anticipated around mid-week next week due to an approaching frontal boundary.

Short Term(Today through Saturday)

Issued at 500 AM AST Thu Dec 18 2025

Calm weather conditions prevailed across the islands overnight. The Doppler Radar detected showers moving across the local waters, windward areas of PR and the USVI overnight, while the leeward areas mainly remained clear. Minimum temperatures ranged from the low to mid-70s along the coast to the low-60s in the mountains and valleys. Winds were primarily from the east with land breeze variations.

A subsiding northerly swell is likely (60 to 80%) to continue producing hazardous breaking waves of 9 to 11 feet and a high likelihood of life- threatening rip currents along exposed north- facing beaches of Puerto Rico and Culebra through much of the day. Beaches along the north-facing shores of Rincon, Aguada, St. John, St. Thomas, and adjacent islands have a high probability (60 to 80%) of experiencing dangerous rip current conditions. While the swell is expected to gradually subside, hazardous coastal and surf conditions may persist into the afternoon, particularly at the most exposed beaches.

Winds are very likely (>80%) to prevail from the east this morning, shifting to east-northeast this evening and into the weekend. As drier air moves into the region and a mid- to upper-level ridge builds overhead, there is a high probability (70 to 80%) of little to no rainfall across most areas during the morning and early afternoon. However, an approaching perturbation is expected to increase cloudiness later today, leading to a low to moderate chance of showers (10 to 40%) across windward areas of Puerto Rico and the U.S. Virgin Islands, and a low to moderate chance (20 to 50%) across interior and western Puerto Rico during the afternoon and evening hours.

From this evening into early Friday morning, increasing moisture will result in a moderate chance of rainfall (40 to 60%) across windward areas. Under these conditions, there is a limited risk of localized flooding across interior and western Puerto Rico this afternoon and evening, followed by a limited flooding risk across north and east windward areas overnight into early Friday.

Looking ahead, model guidance continues to show a high likelihood (>70%) of a strengthening ridge pattern over the Northeast Caribbean, promoting subsidence aloft and a persistent trade-wind inversion. As a result, residents and visitors of PR and the USVI can expect mostly sunny to partly cloudy conditions most of the time, with periodic surges of moisture bringing passing showers, primarily across windward areas and regional waters and, due to local sea-breeze effects, across western Puerto Rico during the afternoons. Overall, daily rain chances are expected to range from low (10 to 20%) to moderate (30 to 50%).

Long Term(Sunday through Thursday)

Issued at 500 AM AST Thu Dec 18 2025

Late in the weekend and into early next week, a weak mid- to upper-level ridge will prevail across the region, supporting generally stable atmospheric conditions. During this period, precipitable water (PWAT) values are expected to remain below to near seasonal climatological levels, ranging from 1.2 to 1.6 inches. At the surface, patches of low-level moisture will continue to move through the area, producing brief passing showers over windward sections of the islands. Rainfall accumulations should remain limited, although isolated afternoon showers may develop across western Puerto Rico. From midweek onward, the mid- level ridge will gradually weaken as a polar trough departing the eastern United States advances from the northwest. This pattern change will increase atmospheric instability, with 500 mb temperatures cooling to below-normal values between -7 and -10 degrees Celsius. A transition toward higher rain chances is anticipated, with moderate probabilities (50 to 60%) for scattered to numerous showers. At the surface, an associated frontal boundary is forecast to approach the region around Wednesday into Thursday (Christmas Eve and Christmas Day) and potentially move across the area. As the front nears, moisture will increase, with PWAT values rising to between 1.5 and 1.8 inches, within the seasonal to above-normal range. The combination of cooler temperatures aloft and increased moisture supports a more unsettled pattern during the holiday period, including scattered showers and isolated thunderstorms. Guidance, including the Galvez-Davison Index, suggests the potential for shallow convection with isolated thunderstorm development. Periods of locally heavy rainfall may occur, which could elevate the risk of localized flooding in flood-prone and poorly drained areas, including ponding on roadways. At this time, the extended forecast indicates a limited flood risk. Also, cooler temperatures are expected in the wake of the possible frontal passage.

AVIATION

(06Z TAFS) Issued at 500 AM AST Thu Dec 18 2025

VFR conditions will prevail through much of the forecast period. SHRA/-SHRA will then form over the interior and western PR (near JBQ) btwn 18/17-23z. Then, a surge of moisture will increase the chance of rain from 18/18z onward over JSJ/IST/ISX. Winds will be calm-light/var thru this morning, then return from the E after 18/13z at 10-15kt with higher gusts and sea breeze variations. Winds will turn more from the ENE from 18/18z onward.

MARINE

Issued at 500 AM AST Thu Dec 18 2025

Moderate to locally fresh east-northeast winds will continue across the local waters today. These winds, combined with additional pulses of a fading northerly swell, will maintain hazardous marine conditions for small craft, particularly across the Atlantic waters and Mona Passage. As a result, Small Craft Advisories remain in effect through at least late tonight and into midday Friday. Another long-period northerly swell is anticipated to arrive and spread across the local Atlantic waters and passages during the weekend, keeping hazardous marine conditions into early next week.

BEACH FORECAST

Issued at 500 AM AST Thu Dec 18 2025

A High Risk of rip currents continues today along the western, northern, and eastern beaches of Puerto Rico, as well as Culebra, St. Thomas, and St. John. This means life-threatening rip currents are likely within the surf zone, and beachgoers should strictly follow the guidance of lifeguards, beach patrol flags, and signs.

Tonight, the risk will decrease to moderate along western Puerto Rico and St. Thomas, while remaining high along northern Puerto Rico and Culebra through early Friday. Moderate conditions are expected Friday into early Saturday; however, beach conditions are forecast to deteriorate again from Saturday afternoon into Sunday due to strengthening winds and another northerly swell spreading across the local Atlantic waters. Stay tuned to the forecast! For specific location information, please visit weather.gov/beach/sju.

SJU WATCHES/WARNINGS/ADVISORIES

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

High Surf Advisory until 6 PM AST this evening for PRZ001-002- 005-008.

High Rip Current Risk through this afternoon for PRZ010.

High Surf Advisory until 6 AM AST early this morning for PRZ010.

High Rip Current Risk until 6 AM AST early this morning for PRZ011-013.

High Surf Advisory until 6 PM AST this evening for PRZ012.

VI...High Rip Current Risk through this afternoon for VIZ001.

AM...Small Craft Advisory until noon AST Friday for AMZ711.

Small Craft Advisory until midnight AST tonight for AMZ712-741.

Small Craft Advisory until 6 AM AST early this morning for AMZ716-723-726-742.