textproduct: San Juan

KEY MESSAGES

Issued at 452 AM AST Sat May 16 2026

* Passing showers will continue to be steered by E to ESE winds towards E and S PR and the USVI to start the morning, followed by afternoon showers and possible isolated t-storms across interior to W-NW PR and downwind of El Yunque and the local islands.

* Above-normal temperatures will persist across the region this weekend, with heat indices reaching the upper 90s to low 100s during peak afternoon hours, especially across urban and coastal areas.

* An upper-level trough will approach the islands tomorrow, Sunday, onward. This can increase the frequency of showers and isolated thunderstorms.

* A moderate risk of rip currents will persist along many north and east facing beaches of Puerto Rico, Vieques, Culebra, and the USVI through much of the forecast period.

* Low concentrations of Saharan dust particles over the region will peak today and late tonight, gradually decreasing afterwards.

Short Term(Today through Monday)

Issued at 452 AM AST Sat May 16 2026

Current satellite derived precipitable water (PWAT) indicate a patch of moisture steered by east to east-southeast winds approaching the region. PWAT values up to 1.74 inches (at normal values) are being detected over the USVI due to this patch of moisture; values gradually decrease westward down to 1.22 inches (below normal values) over western PR. Showers have continued to be steered towards windward areas with at least minimal accumulations detected by radar since midnight over the USVI, Culebra and E to SE PR. Patchy fog is also currently over sectors of interior PR. Lows have been in the mid 70s to around 80 over urban and coastal sectors of the islands, and in the upper 50s to the 60s at higher elevations of PR.

East to east-southeast winds will continue to steer patches of moisture towards the region during the period. PWAT values will be generally at normal values as these patches of moisture move over the region. However they can locally reach above normal values during afternoon convection. Model guidance suggests more frequent interruptions of drier air on Monday. Ridging that was present during the past few days will continue to weaken today as an upper trough approaches the area from the west and amplifies, increasing instability during the period, especially tomorrow and Monday. Showers will continue to be steered towards windward sectors, prompting periods of variable to showery weather with moderate to locally heavy rainfall at times. This can result in ponding of water over roads and poorly drained areas with a chance of urban and small stream flooding. Each afternoon, diurnal heating, local orographic effects and sea breeze convergence will also aid in the development of showers and possible isolated t-storms across interior to west and northwest PR as well as downwind of El Yunque, and the USVI towards eastern PR. As the upper trough continues to approach, instability will also aid in the development of this afternoon convection each day. This can result in a limited to elevated flooding risk. Galvez-Davidson Indices are forecast at up to around 25 today, and at up to 35 to 40, tomorrow, Sunday. The presence of some drier air in the mid-levels can help inhibit this activity. Although rain is expected, the up to breezy east to east-southeast flow will also promote above normal temperatures today and tomorrow, as indicated by 925 mb temperature guidance. Highs will reach the upper 80s to lower 90s across urban and coastal areas while heat indices will exceed 100 to 105 degrees F during the afternoon hours. This will result in a limited to elevated heat risk. Current guidance suggests more high-end normal 925 mb temperatures on Monday, prompting a limited heat risk. Low concentrations of Saharan dust particles over the islands will peak today and late tonight (prompting hazy skies at times), before gradually decreasing tomorrow morning onwards.

Long Term(Tuesday through Saturday)

Issued at 452 AM AST Sat May 16 2026

A gradual transition toward a wetter and somewhat more unstable weather pattern is expected across Puerto Rico and the U.S. Virgin Islands through the latter half of the upcoming workweek. Surface high pressure over the western Atlantic will maintain moderate to locally fresh easterly to east-southeasterly winds, with occasional stronger and gusty periods. Early in the week, conditions should remain relatively quiet overall, with intermittent patches of moisture promoting passing showers across eastern Puerto Rico and the U.S. Virgin Islands, followed by isolated afternoon convection across western Puerto Rico. Rainfall coverage should generally remain more dry than wet, especially across southern and eastern Puerto Rico, which may continue to favor ongoing drought concerns.

At upper levels, a deep trough lingering over the western Atlantic is forecast to gradually sink farther south late in the workweek, supporting enhanced divergence aloft, cooling mid-level temperatures, and a less dry environment across the region. However, moisture continuity through the vertical column still appears somewhat inconsistent, meaning moisture depth and persistence will largely determine daily shower and thunderstorm coverage. By late week, increasing moisture and stronger diurnal heating should support more frequent afternoon showers and thunderstorms across interior and western Puerto Rico, with flooding concerns gradually increasing. Heat concerns will continue through the period, although slightly cooler conditions may develop at times due to increased cloud cover and rainfall activity.

AVIATION

(06Z TAFS) Issued at 452 AM AST Sat May 16 2026

Mainly VFR conditions at the terminals. -SHRA/VCSH will continue to be steered by E to ESE winds and reach windward terminals from time to time. Btwn 16/16-23Z SHRA/+SHRA will develop across interior to NW PR, with isolated TS possible and lines of SHRA also developing from the local islands and El Yunque. This can cause brief MVFR conditions over TJBQ and TJSJ. E to ESE winds up to around 15 kts, with higher gusts and sea breeze variations, decreasing after 16/23Z.

MARINE

Issued at 452 AM AST Sat May 16 2026

A broad surface high pressure over the central Atlantic will promote moderate to locally fresh east to east-southeasterly winds across the regional waters through the weekend. Another surface high pressure building over the western Atlantic will promote more easterly winds early next week. These breezy conditions will maintain somewhat choppy seas, particularly across the offshore and exposed Atlantic and Caribbean waters. Seas are forecast to remain between 4 and 6 feet during the next several days. Afternoon and early evening isolated thunderstorms can be expected each day across the western waters of Puerto Rico.

BEACH FORECAST

Issued at 452 AM AST Sat May 16 2026

A moderate risk of life-threatening rip currents will prevail across the east, north, and southern beaches of Puerto Rico and the U.S. Virgin Islands through early next week. Beach goers should exercise caution when entering these beaches. Life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers.

If you become caught in a rip current, yell for help. Remain calm, do not exhaust yourself and stay afloat while waiting for help. If you have to swim out of a rip current, swim parallel to shore and back toward the beach when possible. Do not attempt to swim directly against a rip current as you will tire quickly.

SJU WATCHES/WARNINGS/ADVISORIES

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