textproduct: San Juan

KEY MESSAGES

Issued at 1028 AM AST Thu Dec 18 2025

* High Surf Advisory conditions will continue along the northern beaches of Puerto Rico and Culebra until this afternoon. Life- threatening rip currents will prevail across the northern exposed beaches of the islands through early Friday due to a lingering northerly swell.

* Another northerly swell and increasing trade winds will cause hazardous seas and life-threatening rip currents again from late Saturday through Sunday.

* A weak surface trough will increase shower activity across the USVI and eastern half of PR from late this afternoon through tonight.

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

Short Term(This afternoon through Saturday)

Issued at 1028 AM AST Thu Dec 18 2025

Mostly sunny to partly cloudy skies prevailed during the morning hours across the islands. Maximum temperatures were in the mid 80s in general across the lower elevations. The wind was from the east to northeast between 12 and 16 mph with gusts between 22 and 26 mph. Streamers were developing around noon over the USVI, and passing showers were increasing from the Anegada Passage and Caribbean waters.

For the rest of this afternoon into tonight, a weak surface trough will cross the region, increasing cloudiness and quick passing showers over the USVI and the eastern half of PR, as well as across the northern and southern coastal areas of the island. Ponding of water in roads and other poor drainage areas can be expected. For Friday and Saturday, more stable conditions and a drier air mass is expected to prevail over the islands under the influence of a building upper level ridge across the central Caribbean. Moderate to fresh trade winds with a northeasterly component will bring quick passing showers with minor rainfall accumulations across the islands at times, particularly across the windward areas. Shallow afternoon convection is possible each afternoon over the SW quadrant of PR, however, rainfall amounts are not expected to cause flood concerns.

Long Term(Sunday through next 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

(18Z TAFS) Issued at 1028 AM AST Thu Dec 18 2025

VFR early in the fcst period. However, a surface trough over the Anegada Passage will cross the local area later this afternoon through tonight. This will increase SHRA over the USVI terminals fm 18/20z-19/03z, at TJSJ fm 19/00z-07z, and fm 19/03-09z at TJBQ/TJPS. Tempo MVFR conds are possible with these showers. For most of the fcst period winds will continue ENE at 10-15 kt with higher gusts at times and sea breeze variations at TJPS til 18/21z.

MARINE

Issued at 1028 AM AST Thu Dec 18 2025

A surface trough moving from the east will increase showers across the regional waters today. A weak surface low northeast of the region near 28N and a surface high pressure over the western Atlantic will promote moderate to locally fresh east to northeast winds during the next few days. These winds, combined with additional pulses of northerly swells, will maintain hazardous seas for small craft, particularly across the Atlantic waters and local passages.

Small Craft Advisories(SCA) are in effect through at least midday Friday. SCA conditions will return late in the weekend across the Atlantic waters and local passages.

BEACH FORECAST

Issued at 1028 AM AST Thu Dec 18 2025

Lingering northerly swell will continue to cause life-threatening rip currents along the north facing beaches of the islands through early Friday. Please follow the guidance of lifeguards, beach patrol flags, and signs.

Another northerly swell and increasing winds will bring large breaking waves during the weekend along the north and eastern beaches of PR and the USVI. Rough surf conditions and life- threatening rip currents are expected once again.

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- 005-008-012.

High Rip Current Risk until 6 PM AST this evening for PRZ010.

VI...High Rip Current Risk until 6 PM AST this evening for VIZ001.

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

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