textproduct: San Juan

KEY MESSAGES

Updated at 207 PM AST Sat Apr 4 2026

* Above-normal moisture and increasing instability will support periods of heavy rainfall through midweek.

* Up to an elevated flooding risk will continue, especially across windward areas overnight and during the afternoon, interior/western/north-western Puerto Rico as well as downwind of El Yunque (towards the metro area) and mainly downwind of the local islands.

* Breezy to locally windy ESE flow and a fading northeasterly swell will persist through early next week, leading to hazardous marine conditions for small craft and a high risk of life- threatening rip currents along northern and eastern beaches.

* Warmer-than-normal temperatures will develop by midweek, with heat indices potentially reaching the low 100s by mid next week.

Short Term(This evening through Monday)

Issued at 207 PM AST Sat Apr 4 2026

In the morning hours, cloudiness and upper cloudiness prevailed across the local islands. At the local waters, the presence of pockets of showers was noted by the Doppler Radar, with some of them streaking along the northern coast of Puerto Rico. Surface winds prevailed from the east, slightly veering to the east-southeast. As of 11 AM, Doppler Radar showed the development of shower activity along the northeastern PR sections, extending into the San Juan Metropolitan area, due to available moisture and local and diurnal effects. The shower activity quickly spread along the Cordillera Central, moving into the western interior, affecting the vicinity of Mayaguez. According to radar rainfall estimates, accumulations ranged from 2 to 3 inches across municipalities between Bayamon and Trujillo Alta, as well as in the western interior. Daytime temperatures rise due to the lack of deep cloudiness, with thermometers along the coast reading 84 to 87, and across the mountains in the low 80s.

For the rest of the day, the broad surface high pressure extending from the central Atlantic into the Caribbean will dominate the surface pattern, promoting an east-southeasterly wind flow across the region. Under this setup, an unsettled weather regime will persist with the influence of a shortwave trough around 700 mb and a strong jet streak at 250 mb exceeding 100 knots. This upper-level support will enhance divergence aloft and promote rising motion across the islands. As a result, shower activity will be scattered, with the main focus across the interior to northwestern Puerto Rico for the rest of the afternoon. Thunderstorm activity is expected with the remaining strong showers and extending into the western coastal local waters. Therefore, periods of moderate rainfall may lead to ponding on roads and reduced visibility, though widespread flooding is not expected. For tonight, High-Resolution models suggest an increase in shower activity along windward sections of Puerto Rico and the U.S. Virgin Islands. This activity is forecast to be between light and moderate.

On Sunday, the surface high pressure will continue to dominate, maintaining an east-southeasterly wind flow while a tightening pressure gradient supports breezy conditions. South winds at 700 mb will enhance moisture transport across the islands, and an increase in relative humidity between the 750500 mb layer will support deeper moisture availability and more efficient cloud development. This setup, combined with precipitable water values in the 75th percentile and the lingering influence of an upper-level jet streak near 70 knots, will favor more persistent and organized shower activity. Expect increased vertical convergence leading to periods of steady rainfall, particularly across eastern and southern Puerto Rico during the morning, shifting toward the interior and northwestern municipalities by the afternoon. By Monday, the surface pattern will evolve as the high pressure combines with a surface disturbance just north of Hispaniola, resulting in a more pronounced southerly wind flow between 850 and 700 MB. Along with westerly winds at 500 mb and a 250 mb jet streak near 60 knots, this will continue to support an active weather pattern. Shower activity will mainly develop across the interior and northern sections of Puerto Rico due to local effects and moisture convergence. However, despite the available moisture, the Galvez-Davison Index (GDI) suggests a lower potential for thunderstorm development. Periods of moderate rainfall may still lead to urban and small stream flooding, particularly in areas experiencing repeated showers.

Long Term(Tuesday through next Friday)

Issued at 318 AM AST Sat Apr 4 2026

A wet and unstable pattern will prevail across the region through much of the long-term period, as a mid- to upper-level trough approaches from the west and settles across the northeastern Caribbean. At the surface, an induced inverted trough near Hispaniola will maintain a persistent southeasterly wind flow across the region. This will promote the advection of abundant tropical moisture into the forecast area, with precipitable water (PWAT) values increasing to near or above 2.0 inches and moisture deepening through the entire column. This southeasterly flow will also support above normal temperatures, with model guidance indicating 925 mb temperatures increasing to near two standard deviations above climatological normals by midweek. As a result, warmer-than-normal conditions are expected at the surface, with heat indices potentially reaching the low 100s for the first time this year in some areas. In addition to the heat impacts, the increased low-level warmth will contribute to greater instability, providing additional fuel for convective development.

Aloft, the presence of the upper-level trough will further enhance instability, with low- to mid-level lapse rates becoming modestly steep for the region. Combined with elevated relative humidity values through the 850-500 mb layer, this will support the development of heavy showers and widespread convective development. Under this pattern, scattered to numerous showers and thunderstorms are expected each day, with activity becoming more widespread during the afternoon hours due to diurnal heating and local effects. The most active period is anticipated Wednesday through Thursday, when the combination of peak moisture, anomalous warmth, and upper-level support will maximize convective coverage. Thunderstorms during this period will be capable of producing heavy rainfall, frequent lightning, and gusty winds. The available heat and instability may also support stronger thunderstorm development, with the potential for intense downpours.

As a result, the risk of urban and small stream flooding will remain elevated, along with the potential for rapid river rises. Saturated soils and elevated streamflows from previous rainfall will further exacerbate flooding impacts, particularly across flood-prone and poor drainage areas.

By Friday onwards, conditions are expected to gradually improve as the upper-level trough weakens and shifts away from the region. Although lingering moisture will continue to support isolated to scattered shower activity, a reduction in overall coverage and intensity is expected, with a transition toward more typical trade wind conditions by late in the period.

AVIATION

(18Z TAFS) Issued at 207 PM AST Sat Apr 4 2026

Mostly VFR conditions will persist with some brief periods of MVFR to IFR for TJPS, TJSJ & TJPS during the TAF period. SFC winds will continue from the E-SE winds up to 15 knots with gusty winds near showers. At 04/18Z, SHRA and TSRA will develop across the mountains and move across TJSJ & TJBQ from 04/18Z-0423Z. This pattern will allow a temporary change in SFC winds, lower VIS, and lower CIGS in the FL020 to FL050. winds will diminish at 05/00Z, becoming lighter up to 8 knots with land breeze variation.

MARINE

Issued at 207 PM AST Sat Apr 4 2026

Hazardous marine conditions are expected to persist through early next week. A strong high-pressure system in the Atlantic will maintain fresh to locally strong easterly winds today, veering to become east-southeasterly late this afternoon through most of the period. When combined with a fading northeasterly swell, seas will remain choppy to rough, particularly across Atlantic waters and local passages. While trade wind showers continue across the region, expect isolated to scattered thunderstorms, especially during the afternoon hours over coastal waters, especially near western and northwestern Puerto Rico. Coverage may increase slightly over the weekend as an upper-level trough arrives, interacting with abundant tropical moisture.

BEACH FORECAST

Issued at 207 PM AST Sat Apr 4 2026

A High Risk of Rip Currents (life-threatening rip currents are likely in the surf zone) is in effect for the northern and eastern coastlines of Puerto Rico, Vieques, Culebra and the USVI through the rest of the weekend. Breaking waves can reach 6 to 9 feet, particularly over the northern coastline of Puerto Rico. This is due to a subsiding northeasterly swell and breezy to locally windy condtions.

Although hazards will gradually subside, a high rip current risk will persist for most of these areas through Monday. Beachgoers and inexperienced surfers are strongly urged to stay out of the water. Up to a moderate risk of rip currents is forecast Tuesday and Wednesday, before increasing to high again by Thursday.

Beachgoers and inexperienced surfers are urged to avoid going into the water, walking over rocks or jetties, as life- threatening rip currents are very likely. Heed the advice of lifeguards, beach patrol flags, and signs. Access to hazardous beaches may be limited, and individuals should follow all posted warnings and safety guidance.

Visitors should also be mindful of the weather, in addition to surf hazards. In addition to the life- threatening rip currents, beachgoers should stay weather alert due to isolated showers and thunderstorms capable to produce gusty winds, periods of heavy showers, and lightning. If thunder is heard, immediately seek refuge inside a sturdy building.

HYDROLOGY

Issued at 318 AM AST Sat Apr 4 2026

Hydrologic conditions will become increasingly favorable for flooding impacts through much of the forecast period. Elevated moisture (PWAT 2.0 inches), increasing instability, and efficient warm-rain processes will support periods of heavy rainfall.

Flooding is not expected to be widespread; however, there is an elevated risk of urban and small stream flooding, especially in areas experiencing repeated or slow-moving showers. The highest risk will occur overnight across windward areas and during the afternoon across interior and western Puerto Rico.

Recent rainfall has resulted in saturated soils across portions of eastern and northern Puerto Rico, increasing runoff efficiency and the likelihood of rapid rises in streams and rivers, particularly in steep terrain.

The flooding risk is expected to increase from this afternoon through midweek, with the potential for isolated flash flooding, especially during the peak period from Wednesday through Thursday.

Conditions should gradually improve late in the week as moisture decreases and instability weakens.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Monday afternoon for PRZ001-002- 005-008-012.

High Rip Current Risk through late Sunday night for PRZ010-013.

VI...High Rip Current Risk through Monday afternoon for VIZ002.

High Rip Current Risk through late Sunday night for VIZ001.

AM...Small Craft Advisory until 6 PM AST Monday for AMZ711.

Small Craft Advisory until 6 AM AST Monday for AMZ712-716.

Small Craft Advisory until noon AST Monday for AMZ723.

Small Craft Advisory until 6 PM AST Sunday for AMZ741.

Small Craft Advisory until noon AST Sunday for AMZ742.