textproduct: San Juan

KEY MESSAGES

Updated at 250 AM AST Fri Apr 17 2026

* Another active afternoon is forecast today, with some instability present and sufficient moisture across the area. Therefore, a limited to elevated flooding risk is expected.

* More stable conditions are expected on Sunday, with drier air and warmer Temperatures aloft limiting widespread shower activity.Therefore, a typical trade wind pattern will prevail, bringing passing morning showers to eastern Puerto Rico and the U.S. Virgin Islands, followed by isolated afternoon convection over western Puerto Rico.

* A moderate risk of rip currents will persist across several beaches, particularly along exposed coastal areas, creating hazardous conditions for swimmers.

* The U.S.Virgin Islands will experience variable weather conditions today, with periods of passing showers, followed by gradual improvement into Sunday and continuing into the upcoming workweek.

Short Term(Today through Sunday)

Issued at 250 AM AST Fri Apr 17 2026

During the overnight hours, weather conditions were variable, with showers mainly affecting the local waters and some moving across southeastern sections of the island. As of 2 AM, showers were brushing the coastal areas of Vieques and St. Croix, with minimal rainfall accumulations reported. Winds prevailed from the east- southeast at speeds of 10 mph or less. Temperatures during the night ranged from the mid to upper 70s along coastal areas, while cooler conditions were observed across the mountainous regions.

Today, as the upper-level trough amplifies over the western Atlantic and shifts eastward away from the area, the forecast area will remain under its divergent side to the southeast, supporting favorable conditions for vertical development. This pattern is reinforced by cooler temperatures aloft and relatively moist conditions through the mid-levels, which will help sustain cloud development and shower activity. Model guidance continues to indicate above-normal moisture levels, with precipitable water remaining elevated compared to climatology. Additionally, mid- level instability suggests a moderately unstable environment, allowing deeper convection, particularly during the peak of the diurnal heating. At the same time, some variability in mid-level moisture is expected, which may briefly limit coverage at times; however, overall conditions remain conducive for scattered showers. The presence of modest low-level flow will aid in steering activity while maintaining convergence along local effects and terrain features. Winds are gradually becoming more easterly. Given these conditions, today will follow a seasonal pattern, with passing showers across windward areas in the morning, followed by a more active afternoon driven by diurnal heating and local effects. Shower activity will concentrate across the Cordillera Central and northwestern interior, where periods of moderate to locally heavy rainfall are possible. As a result, an elevated flooding risk will persist, particularly in urban, low-lying, and poor drainage areas, where repeated showers could lead to ponding of water and minor flooding.

By Saturday, a transition toward a drier and more stable pattern will become more evident across the forecast area. Mid-level moisture is expected to decrease compared to today, with relative humidity values lowering across the 700500 mb layer, while subsidence associated with the shifting upper-level trough will promote warming aloft and limit vertical development. Although sufficient low-level moisture will remain to support passing morning showers, particularly across eastern Puerto Rico and the U.S. Virgin Islands, overall coverage should be reduced. During the afternoon, localized convection may still develop across the western interior of Puerto Rico; however, activity should remain less organized and shorter-lived due to weaker instability and reduced lapse rates. Winds will continue from the east to east- southeast, supporting typical diurnal patterns. As a result, flooding concerns should diminish compared to today, with only isolated ponding possible in areas that receive brief, heavier showers.

On Sunday, similar to Saturday, a stable weather pattern is expected. Mid-level conditions will remain relatively drier compared to previous days, with warming aloft promoting increased stability and limiting vertical cloud development. Although patches of low-level moisture will continue to move across the area within the easterly wind flow, overall moisture availability will remain closer to seasonal levels, reducing the potential for widespread shower activity. At the surface, a strengthening high pressure system over the central Atlantic will maintain a steady easterly to east-southeasterly wind flow, supporting typical trade wind conditions. This pattern will favor passing showers during the overnight and morning hours across eastern Puerto Rico and the U.S. Virgin Islands, followed by localized afternoon convection across the interior and western sections of Puerto Rico driven mainly by diurnal heating and local effects; however, activity should remain limited in coverage and intensity due to the more stable atmospheric profile. As a result, flooding concerns will continue to decrease, with only isolated ponding possible in areas that experience brief, heavier showers, and overall conditions will resemble a typical seasonal pattern with reduced convective activity across the region.

Long Term(Monday through Friday)

Issued at 250 AM AST Fri Apr 17 2026

he forecast remains on track with no significant changes from the previous discussion. As the influence of the upper-level trough weakens and exits the northeastern Caribbean, drier and more stable conditions are expected to return. A mid-level ridge will build over the area, bringing a stable air mass aloft. At the surface, a dominant high pressure system over the central Atlantic will maintain light to moderate easterly winds through mid-week. During the first half of the period, precipitable water (PWAT) values will drop to seasonal normals of approximately 1.50 inches and are expected to remain within that range for the rest of the workweek.

Local conditions will stay seasonal, with occasional showers moving into the eastern portions of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands during the morning hours. This will be followed by afternoon convective activity across the interior and western portions of Puerto Rico. This afternoon activity could result in moderate to heavy rainfall and isolated thunderstorms due to the combination of available moisture, daytime heating, and local effects. Temperatures at 500 mb are expected to remain within seasonal values of -6C to -8C; therefore, a thunderstorm or two cannot be ruled out. Due to previous rainfall, soil saturation, and elevated river levels, the potential for flooding persists. Temperatures at 925 mb will remain seasonal through most of the period, with highs in the low to mid-80s across coastal and urban areas and the upper 70s to low 80s in the higher mountains.

AVIATION

(06Z TAFS) Issued at 250 AM AST Fri Apr 17 2026

Mainly VFR conditions prevail, with brief MVFR possible in SHRA over eastern terminals. SHRA brushing TISX are resulting in lower CIGs.SHRA and isolated TSRA developing during the afternoon over the interior and western sections, including from 17/18Z to 17/23Z, will result in periods of MVFR conditions with reductions in VIS. Winds will remain light and variable early, becoming east to east-southeast at 812 knots after 17/14Z. Gusty winds are possible near SHRA/TSRA and with sea breeze variations.

MARINE

Issued at 250 AM AST Fri Apr 17 2026

A mid-to upper-level trough will maintain an unstable weather pattern across the regional waters, resulting in periods of strong t- storms through at least Saturday. A surface high over the western to central Atlantic will promote moderate to locally fresh east to southeast winds, in turn resulting in moderate to choppy seas through at least early next week. A small northeasterly swell will also continue to propagate across the Atlantic waters and Caribbean passages through early next week, contributing to hazardous marine conditions at times. T-storms can produce locally higher winds, frequent lightning, and reduced visibility.

BEACH FORECAST

Issued at 250 AM AST Fri Apr 17 2026

Up to a moderate risk of rip currents (life-threatening rip currents are possible in the surf zone) will be in effect through the weekend, especially along north and east facing beaches of Puerto Rico and the U.S. Virgin Islands. A long period northerly swell may arrive by the next midweek, potentially deteriorating coastal conditions. Beachgoers should remain alert for afternoon showers and isolated t-storms.

SJU WATCHES/WARNINGS/ADVISORIES

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