textproduct: San Juan

KEY MESSAGES

Issued at 258 PM AST Sat Mar 28 2026

* Elevated flooding risk through the forecast period in Puerto Rico: Repeated showers and thunderstorms may produce rapid water rises in urban areas, small streams, and flood-prone locations, with a risk of landslides in steep terrain.

* Localized flooding in the U.S. Virgin Islands: Passing showers and isolated thunderstorms may cause water to pond on roads and in low-lying areas, creating hazardous travel conditions.

* Daily afternoon thunderstorms expected: Thunderstorm development each afternoon will increase the risk of localized flooding and lightning hazards, especially in interior and western areas.

* Deteriorating marine and coastal conditions midweek: A long- period northerly swell arriving late Monday night through at least Thursday will lead to hazardous surf, increased rip current risk, and possible Small Craft Advisory conditions.

Short Term(This evening through Monday)

Issued at 258 PM AST Sat Mar 28 2026

During the morning hours, most of the activity remains over the Atlantic Offshore waters. Meanwhile, by mid-morning, rainfall in the US Virgin Islands and Puerto Rico began to increase, with heavy rain affecting the northern USVI, where Flood Advisories were issued, as well as across the El Yunque Mountains near Fajardo, Ceiba, and Naguabo, and for south PR from Ponce to Sabana Grande. The Doppler Radar detected a strong convection along the Cordillera Central and other portions in St Croix, Vieques, Culebra, and PR. Maximum temperatures were in the mid-80s across urban and coastal areas, and in the upper 70s in the mountains. Winds were mainly from the northeast at 5 to 15 mph, with sea- breeze variations and higher gusts.

The afternoon convection will persist through this evening. With saturated soils and elevated rivers, the flooding risk will remain elevated in some locations in PR, especially along the Cordillera Central and in southern PR. to pose a flooding risk during the period. Convection will gradually diminish overnight, though showers and isolated thunderstorms will reform across the Atlantic Waters and Caribbean Waters near the Anegada Passage, and some of these showers will occasionally affect the northern and eastern windward locations of PR and the US Virgin Islands.

A drier air mass will move in over the islands around Sunday, reducing the coverage and longevity of the convection. Regardless of this, under a northeasterly wind flow, pockets of moisture will arrive at times over the windward locations in PR and the USVI, followed by afternoon convection across portions of the interior and southwest quadrant of PR, supported by local effects, a lingering upper-level trough, and sea breeze variations.

As winds increase around Monday, moisture pooling will increase over the region, potentially increasing the potential for showers and thunderstorms, especially during the afternoon.

LONG TERM

Issued at 417 AM AST Sat Mar 28 2026

Strong low to mid level high pressure will maintain a strong northeasterly wind flow through much of the workweek. The steering flow is expected to be at 15 to 25 kts. At the upper level, the jet stream will maintain speeds of nearly 80 knots. Under the low level winds, weak disturbances will stream at times across the islands. This will maintain the probability of precipitation on the medium and high side. In general, showery weather will persist for most of the Virgin Islands and eastern Puerto Rico. Then, in the afternoon, diurnal heating will trigger showers and thunderstorm along the interior and western Puerto Rico. Because the winds are expected to be strong, the risk of flooding will be mostly limited. Impacts may include hazardous driving conditions due to low visibility and ponding of water. In the west, urban and small stream flooding could still occur, although not widespread.

AVIATION

(18Z TAFS) Issued at 258 PM AST Sat Mar 28 2026

All TAF sites should experience VRB conds. Aft convection will bring -TSRA/+TSRA across PR, with TEMPOs in JBQ, JSJ, JPS, ISX, and IST btwn 28/18-22z, reducing VIS and leading to MVFR conds. Winds will weaken and become light and VRB aft 28/22z, strengthening by 29/12Z, expect E winds btwn 10-15 kt with higher gusts at times.

MARINE

Issued at 258 PM AST Sat Mar 28 2026

An unstable weather pattern will persist in the region through this evening, leading to scattered showers and isolated thunderstorms. A surface inverted trough located north of the area will sustain light to moderate east-northeast winds at least until Sunday, with winds increasing to moderate to fresh by Sunday afternoon, resulting in choppy seas. Additionally, winds will pick up after a cold front moves toward the region from the Western Atlantic by Monday. Furthermore, another long-period northerly swell will create hazardous marine conditions, expected to last until at least Thursday. These conditions may be dangerous for small craft operators.

BEACH FORECAST

Issued at 258 PM AST Sat Mar 28 2026

A moderate risk of rip currents is expected along north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands, while a low risk will persist along south-facing beaches.

Conditions are expected to worsen from Monday night through Thursday due to the arrival of a long-period northerly swell combined with increasing winds. This combination is likely to create life-threatening rip currents and dangerous surf conditions along the north-facing exposed coastlines.

Beachgoers should exercise caution and remain aware of changing marine conditions. Always swim near a lifeguard and follow local safety guidance.

SJU WATCHES/WARNINGS/ADVISORIES

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