textproduct: San Juan

KEY MESSAGES

Issued at 242 PM AST Fri Mar 20 2026

* For the rest of the afternoon, showers may develop across interior and western Puerto Rico, but no significant impacts are expected.

* Across the U.S. Virgin Islands, expect generally fair weather with passing trade wind showers at times.

* A moderate risk of rip currents will continue along north and east- facing beaches through the weekend.

* A frontal boundary approaching from the northwest will bring increasing showers and a more unsettled weather pattern from Saturday into early next week.

* Periods of heavy rain and thunderstorms may lead to localized flooding, lightning hazards, and hazardous marine and beach conditions.

Short Term(This evening through Sunday)

Issued at 242 PM AST Fri Mar 20 2026

Mostly tranquil conditions have prevailed through much of the day, with the exception of a few passing showers across eastern and southeastern Puerto Rico. The 12Z morning sounding indicated a precipitable water (PWAT) value of 1.15 inches, which is below average. Daytime high temperatures have been warm, ranging from the mid to upper 80s across coastal areas to the low 90s, while the mountainous regions have remained in the upper 70s. For the remainder of the afternoon, showers may develop across the interior and western portions of Puerto Rico, however, no flooding impacts are expected.

Over the weekend, a transition to a wetter and more unsettled pattern is expected. Despite the increase in tropical moisture associated with southerly flow, model guidance continues to suggest limited overall rainfall accumulations on Saturday. The wettest conditions, or strongest model signal, are currently expected on Sunday as the front settles over the region. Latest model guidance and satellite-derived PWAT data indicate moisture trailing from frontal boundary to the northwest, forecast to move into the northeastern Caribbean late tonight into Saturday morning. PWAT values will then increase through Sunday, rising from around 1.00 inch today to nearly 1.80 inches through Sunday (around the 75th percentile, above normal for this time of year). Another factor to note, is that winds will remain around 10 knots or less as the local pressure gradient weakens, particularly on Sunday. This combination of increased moisture and weak steering flow will favor slow-moving showers and as a consequence an elevated flooding risk, especially in urban areas, roads, small streams, and poor drainage areas as the potential for greater accumulations increases. The U.S. Virgin Islands will remain on the drier side of the frontal boundary through early Saturday, with shower coverage gradually increasing by Sunday.

Overall, rainfall activity is expected to remain variable on Saturday, with only isolated to scattered showers and less impacts. By Sunday, more widespread and persistent rainfall is anticipated, increasing the potential for localized flooding across Puerto Rico.

LONG TERM...(Monday through Friday)

Issued at 211 AM AST Fri Mar 20 2026

A broad mid to upper level trough pattern will persist across the western Atlantic and northeastern Caribbean through much of the workweek. A jet streak near the region at the start of the period will provide enhanced divergence aloft and support generally unstable conditions, weakening slightly and lifting northward later in the week but remaining close enough to influence the local area. At the surface, high pressure building over the western Atlantic will promote a transition to northeasterly winds early in the week, persisting through midweek and supporting a cooler and more stable low-level flow. Moisture will remain near to above normal, initially extending to around the mid levels and becoming deeper by midweek onward, despite occasional intrusions of drier air aloft. Weak mid- level perturbations early in the period will gradually lift northward, while a surface-induced trough or trade wind perturbation associated with a mid-level disturbance may approach the region later in the week, enhancing low-level convergence.

Unsettled weather conditions will persist through the workweek, with hazards initially focused on excessive rainfall and thunderstorms. Early in the period, lighter steering flow and sufficient moisture will favor slow-moving showers, increasing the risk of urban and small stream flooding, along with frequent lightning. As northeasterly winds become established, showers will favor windward areas, with afternoon convection over interior and western Puerto Rico. From midweek onward, deeper moisture and continued upper-level support will lead to more efficient rainfall processes, maintaining an elevated flooding risk. In addition, the wind threat may increase later in the week as stronger low-level flow and passing perturbations support periods of gusty winds, particularly in and near heavier showers and thunderstorms.

AVIATION

(18Z TAFS) Issued at 242 PM AST Fri Mar 20 2026

Mainly VFR conds expected to prevail across all TAF sites. VCSH and brief -RA possible, mainly ovr W PR and and within streamers downwind of the TIST, leading to brief MVFR conds possible. TJPS and TJSJ have the better chance to observe VCSH/-RA overnight and Sat morning. Sfc SE to S winds at 10-12 kts or less with sea breeze variations and occasional higher gusts. Winds bcm lighter/vrb overnight, then incr to 10-12 kts again aft 21/13Z.

MARINE

Issued at 242 PM AST Fri Mar 20 2026

Light to moderate southeast winds will prevail across the regional waters in the short term. Choppy seas may persist across portions of the Atlantic waters due to moderate to locally fresh winds, and small craft should continue to exercise caution. As a pre-frontal trough and associated frontal boundary approach the region from the northwest, winds will weaken and shift from the southeast to southerly through the weekend, becoming light and variable at times. However, this boundary could promote localized hazardous marine conditions, particularly across the Atlantic waters and the Mona Passage. As high pressure builds over the western Atlantic early next week, winds will turn northeasterly and increase, resulting in deteriorating marine conditions once again. Unsettled weather will develop from the weekend into early next week, leading to increased shower activity across the local waters.

BEACH FORECAST

Issued at 242 PM AST Fri Mar 20 2026

Beach conditions have begun to improve, as winds and seas have gradually decreased across the coastal waters. Nevertheless, we urge visitors and residents to remain alert and monitor the forecast for updates or changes, as a MODERATE risk of rip currents persists along the northern and eastern beaches of Puerto Rico, Vieques, Culebra, and the US Virgin Islands through the weekend. A moderate risk means that life-threatening rip currents are still possible in the surf zone, and beachgoers should remain alert and exercise caution. A low risk is expected along more protected southern beaches.

In addition, the development of heavy showers and isolated thunderstorm activity associated with an approaching frontal boundary may result in localized hazardous beach conditions, including reduced visibility, gusty winds, dangerous surf, and lightning. Thunderstorms will pose a significant lightning risk, particularly for those in or near the water, and beachgoers should be prepared to seek shelter quickly if storms develop.

For additional information and location-specific rip current details, please visit: weather.gov/beach/sju.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.