textproduct: San Juan

KEY MESSAGES

Issued at 231 PM AST Sun Aug 16 2026

- A heat threat will persist through most of the workweek due to warm temperatures and heat indices ranging between 108 and 111 degrees.

- A drier weather pattern is expected from Monday through Wednesday as a generally drier air mass dominates the region. No significant rainfall accumulations are anticipated during the first part of the week. However, by Wednesday, an increase in moisture is forecast, leading to a greater potential for showers and a limited flooding risk, particularly across western portions of Puerto Rico.

- By Thursday into Friday, a wetter and more unstable pattern is expected as a tropical wave moves across the region. Current guidance suggests an increase in shower and thunderstorm activity during this period.

- A Low to Moderate Risk of Rip Currents is expected across the local beaches throughout the workweek.

Short Term(This evening through Tuesday)

Issued at 231 PM AST Sun Aug 16 2026

Fair weather conditions with partly cloudy skies prevailed this morning as the tropical wave moved away from the region. Temperatures are ranging from the upper 80s to low 90s F across urban and coastal areas, while temperatures are in the 70s to low 80s F in the mountainous regions. Conditions are breezy with gusty periods, with maximum winds of 15 to 20 mph and gusts ranging from 20 to 29 mph, particularly near coastal stations. Moderate concentrations of Saharan dust are also present across the region.

In the wake of the tropical wave, drier air has been filtering into the region. The latest GOES-19 precipitable water imagery is showing values around 1.4 to 1.6 inches, which are seasonal to below normal. Combined with stable and dry conditions aloft, shower activity will remain limited for the rest of today and Monday. However, daytime heating and local effects could still trigger localized afternoon showers across western Puerto Rico, but no flood risk is anticipated. Easterly winds will gradually subside tonight and throughout the rest of the short-term period as the pressure gradient loosens across the Caribbean, with easterly to northeasterly winds becoming more seasonal, around 10 to 15 knots.

By Tuesday afternoon, precipitable water (PWAT) values will gradually increase toward more seasonal levels, which could result in better coverage of afternoon showers across western Puerto Rico. In addition, lighter winds could lead to slower-moving showers and allow for some accumulation, particularly during the afternoon. Therefore, a limited flood risk is anticipated across western Puerto Rico on Tuesday afternoon.

A Heat Advisory remains in effect until 5 PM AST this afternoon. The outlook for the short-term period in terms of heat is that an elevated heat risk will persist, as reflected by above-normal 925-mb temperatures, plenty of sunshine, and overall limited rainfall and cloud cover. The recommendation is to remain hydrated and wear light- colored clothing to limit the effects of heat-related illnesses.

Long Term(Wednesday through next Saturday)

Issued at 231 PM AST Sun Aug 16 2026

Variable conditions are still expected in the long-term, with high uncertainty during the second part of the workweek. A surface high pressure building over the Western Atlantic should maintain winds mainly from the E-ENE (shifting briefly from the E-SE on Thursday) throughout most of the period, leading to breezy to locally windy conditions. The latest global solutions indicate a tropical wave (former AL94) approaching the Caribbean Basin and moving across the CWA late Wednesday night into Thursday. According to the deterministic guidance of the ECMWF and GFS, PWAT values may increase to 2.0 - 2.2 inches, with a low chance of reaching 2.2 - 2.4 inches. Additionally, members of the grand ensemble are trending toward wetter values during Thursday, with moisture content in the low and mid levels reaching above climatological normal (around 80%). Under that pattern, lines of strong showers and thunderstorms could move over windward sections of the islands throughout all day, with afternoon convection over interior and western/northwestern Puerto Rico. Rainfall accumulations could lead to ponding of water over roadways and poorly drained areas, along with minor flooding. Nevertheless, theres high uncertainty as the tropical wave encounters unfavorable conditions such as drier airmass, Saharan Dust, and strong wind shear. Although the NHC has ended , residents and visitors should continue to monitor this system. As the tropical wave moves out of the local area, a dry slot, along with concentrations of Saharan Dust, should filter into the region, with PWAT values dropping to below normal (1.2 - 1.4 inches). Although daytime heating and local effects may enhance afternoon convection, showers and isolated thunderstorms could move over western Puerto Rico, though rainfall accumulations will remain limited. By Saturday, a perturbation in the trades, along with an upper-level low, may increase moisture content across the CWA, with PWAT values reaching typical values for this time of the year (between 1.6 and 1.8 inches). This may introduce some instability and enhance convection across the area once again, as the frequency of showers and thunderstorms may increase over windward sections.

AVIATION

(18Z TAFS) Issued at 231 PM AST Sun Aug 16 2026

Mainly VFR conds across TAF sites. Moderate concentrations of Saharan dust are resulting in slight VIS reductions at least thru this evening, then low concentrations the rest of the forecast period. Breezy conditions with occasional gusts up to 28kts, winds slightly reducing overnight, and picking up to 15 kts with gust 25 kts aft 17/14Z. VCSH possible overnight across USVI sites and TJSJ, but overall no significant impacts.

MARINE

Issued at 231 PM AST Sun Aug 16 2026

Hazardous marine conditions will persist through the rest of the afternoon and into the evening hours due to breezy conditions associated with a tight pressure gradient generated by a surface high over the central Atlantic. By Monday morning, easterly winds will become more moderate, allowing seas to gradually subside to 3 to 5 feet, with occasionally higher seas across localized areas. Limited shower activity is expected from Monday through Wednesday. However, by late Wednesday into Thursday, localized hazardous marine conditions may develop with the arrival of a tropical wave previously known as Invest 94L. Mariners are urged to exercise caution, particularly across the offshore waters due to strong thunderstorms and gusty winds.

BEACH FORECAST

Issued at 231 PM AST Sun Aug 16 2026

Hazardous coastal conditions will persist through the rest of the day and into the evening hours due to breezy conditions. Therefore, a High Risk of Rip Currents remains in effect for beaches along the northern, eastern, and southern coasts of Puerto Rico, including Vieques and Culebra, as well as the U.S. Virgin Islands. Improving conditions are forecast by Monday morning, with a Moderate Risk of Rip Currents expected to prevail through much of the workweek, potentially decreasing to a Low Risk by Wednesday. Limited shower activity is expected from Monday through Wednesday. However, by late Wednesday into Thursday, localized hazardous coastal conditions may develop with the arrival of a tropical wave previously known as Invest 94L. Beachgoers are urged to exercise caution along the shoreline due to strong thunderstorms and gusty winds.

FIRE WEATHER

Issued at 231 PM AST Sun Aug 16 2026

Critical fuel conditions continue to persist across the islands, with extreme drought conditions across portions of the southern coastal plains and eastern Puerto Rico. In the wake of the tropical wave, a drier airmass is present, resulting in relative humidity values near or below critical levels. These conditions, combined with little to no rainfall, ongoing rainfall deficits, stressed vegetation, and dry fuels, will maintain conditions favorable for rapid fire spread. The greatest concern remains across southern and southwestern Puerto Rico, where fuels are particularly dry and recent fire activity has been more frequent. A Fire Danger Statement remains in effect until 5 PM AST this afternoon. Residents and visitors are encouraged to avoid outdoor burning. Continue to monitor the forecast, as additional fire weather products may be needed in the coming days.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through late tonight for PRZ001>003-005- 007-008-011>013.

Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013.

VI...High Rip Current Risk through late tonight for VIZ001-002.

Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...Small Craft Advisory until midnight AST tonight for AMZ711-733- 735-741.