textproduct: San Juan

KEY MESSAGES

Updated at 457 AM AST Fri Apr 10 2026

* A High Risk of Rip Currents is in effect for the northern coast of Puerto Rico and Culebra through the weekend due to a long-period, northwest to northerly swell.

* Generally stable weather is forecast through Saturday, with isolated showers over windward areas and afternoon convection over mainly interior to W-NW PR.

* An approaching mid to upper level trough will result in a wetter and more unstable pattern with an increased flooding risk as it reaches the islands late Sunday into the next workweek.

* A limited heat threat will be present today and tomorrow, mainly in coastal and urban areas.

Short Term(Today through Sunday)

Issued at 457 AM AST Fri Apr 10 2026

Since midnight, radar estimated rainfall accumulations showed minimal amounts over eastern PR, Vieques and then northern USVI. The strongest observed shower/t-storm remained over the western offshore Atlantic waters. Official and unofficial stations reported minimum temperatures in the 70s across coastal areas, with some isolated stations reporting 78 to 80 degrees, and in the 60s across interior PR.

Current satellite derived precipitable water (PWAT) values indicate a band of moisture that arrived during the overnight hours and promoted the above mentioned showers, with values up to 1.65 in (at normal values for this time of the year). A broad surface high over the central Atlantic interacting with a frontal low over the western Atlantic, and then another building high over the western Atlantic to end the short term period will continue to result in E to ESE steering flow. 925 wind speeds are forecast to continue up to around 15 kts, normal for this time of the year. Today, Friday, is forecast to be the driest day in the short term period. E to ESE steering flow will steer patches of moisture and drier air towards the area. Satellite imagery already detects the patch of drier air (PWAT values below 1.5 in) that will move over the islands later today and is forecast to be over western PR by this afternoon, serving to limit afternoon convection. Afternoon showers are still forecast over mainly interior to W-NW PR due to diurnal heating, local orographic effects and sea breeze convergence. Showers will also continue to reach windward sectors of the islands. 500 mb temperatures, 250 mb heights, 700 to 500 mb relative humidities will be at normal values, promoting stability and inhibiting shower and t- storm development. Moisture will continue to be steered towards the islands during the period. PWAT values will increase to high end normal to above normal values (above 1.75 in) on Saturday and Sunday while 500 mb temperatures cool and 250 mb heights decrease.

For tomorrow, Saturday, an enhanced pattern will be present with a limited flooding risk forecast during the afternoon over W-NW PR due to convective showers and t-storms. Showers can also develop downwind of the local islands. Advective showers will also continue to reach windward sectors of the islands during the morning and overnight hours. A mid to upper level trough is forecast to approach the region from the E/NE on Sunday, reaching the islands late Sunday into Monday. This will make Sunday a transition day toward a wetter and more unstable pattern forecast during the long term period. This will result in an increase in shower frequency over windward sectors during the morning and enhanced afternoon showers and t-storms, a limited flooding risk will persist to end the weekend but can be increased to an enhanced flooding risk. Showers and isolated t- storms can also reach windward sectors Sunday night and into the long term period. Galvez- Davison Index (GDI) values are forecast at up to 15 today, up to 30 to 35 on Saturday and up to 40 on Sunday. For additional details, including rainfall expectations and hydrologic conditions Sunday onwards, refer to the Hydrologic Outlook (ESFSJU). Patchy fog over will be present during the overnight hours over areas of the interior. Satellite and model guidance also suggest low concentrations of Saharan Dust persisting through the short term period. 925 mb temperatures are forecast to be warmer than normal, with highs reaching the upper 80s to around 90 at urban and coastal areas. A limited heat risk will persist, today and Saturday.

Long Term(Monday through Friday)

Issued at 457 AM AST Fri Apr 10 2026

A wetter and more unstable pattern will develop Monday and persist through midweek as a deep-layered trough and developing upper-level low remain northwest of the region, supporting favorable divergence aloft through at least Tuesday night. Deep moisture will surge into the area from the east on Monday, with precipitable water values exceeding climatological maxima before organizing into a moisture band that lingers over the region Tuesday into Wednesday, then gradually shifts southwestward into the Caribbean by Thursday. Low- level winds will veer from EENE Monday to ESE by midweek, supporting a transition from a more typical diurnal pattern early Monday to increasingly widespread and organized convection Monday afternoon through at least Tuesday, and possibly into Wednesday. Cooler temperatures aloft through Tuesday night will enhance instability, followed by gradual warming by Wednesday into Thursday, leading to a slow decrease in convective intensity, although a moist column will persist.

The primary concern is an elevated to locally significant flooding risk, increasing Monday afternoon and peaking Tuesday into Wednesday. Periods of heavy and repeated rainfall may result in urban and small stream flooding, isolated flash flooding, and localized landslides or rapid river rises. Slower storm motion, particularly on Tuesday, could enhance rainfall totals in affected areas. Model guidance has been consistent in highlighting this event, including the ECMWF Extreme Forecast Index, which indicates anomalously high rainfall potential building Monday, peaking Tuesday into Wednesday, and diminishing by Thursday. Although activity should become less organized late in the period, above-normal moisture will continue to support scattered showers with localized impacts. Confidence is moderate to locally high in the overall pattern, though some uncertainty remains in the exact placement of the heaviest rainfall.

For additional details, including rainfall expectations and hydrologic conditions, refer to the Hydrologic Outlook (ESFSJU).

AVIATION

(06Z TAFS) Issued at 457 AM AST Fri Apr 10 2026

Mainly VFR conditions. E to ESE, at times, light and variable winds to up to 11 kts through 10/13Z, then increasing to around 15 kts with higher gusts and seas breeze variations. VCSH/-SHRA over eastern terminals through the period. SHRA then near or at JBQ at 10/17-22Z. Winds decreasing again after 10/23z.

MARINE

Issued at 457 AM AST Fri Apr 10 2026

Winds will turn more easterly from today and through the weekend as a broad surface high pressure builds from the Central Atlantic. A 4 to 5 feet northwest to north swell will spread across the Atlantic waters and passages, building seas up to 6 feet for the next few days. Therefore, small craft should continue to exercise caution, mainly over the Atlantic Waters. Another pulse of the northerly swell is expected on Sunday. By early next week, a frontal boundary and a pre- frontal trough will increase showers and thunderstorms across the regional waters. Increasing winds and seas building up to 7 feet are also expected, and Small Craft Advisories could be issued for the Atlantic waters during this period.

BEACH FORECAST

Issued at 457 AM AST Fri Apr 10 2026

A 4 to 5 feet long-period, northwest to northerly swell will gradually spread across the Atlantic waters and passages today. This will keep an elevated threat of life-threatening rip currents along the Atlantic beaches of Puerto Rico and Culebra, where a High Rip Current Risk remains in effect through the weekend. By early Sunday, another pulse from the northerly swell is expected to reach the northern exposed coastal waters. Across the USVI, Vieques, and the south facing beaches of PR, up to a moderate risk of rip currents is expected to prevail through the same period.

SJU WATCHES/WARNINGS/ADVISORIES

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

High Rip Current Risk through Saturday afternoon for PRZ012.

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