textproduct: San Juan

KEY MESSAGES

Updated at 238 AM AST Mon May 4 2026

* Mostly fair weather will prevail, with isolated afternoon showers over interior and northwestern Puerto Rico today.

* An approaching trough Tuesday and Wednesday may support localized afternoon showers, with brief heavy rainfall possible. Isolated thunderstorms cannot be ruled out, though activity will remain limited.

* Warmer-than-normal temperatures will persist, with heat indices reaching or exceeding 100F across urban and coastal areas.

* Moderate rip current risk will continue along north- and east- facing beaches of the islands at times.

Short Term(Today through Wednesday)

Issued at 238 AM AST Mon May 4 2026

A generally stable weather pattern will prevail today, followed by a slight increase in instability by Tuesday and Wednesday as a weak polar trough approaches from the west.

For today, ridging aloft and mid-level drying will dominate the local weather pattern. At the surface, high pressure over the central Atlantic will promote an east-southeasterly wind flow across the region. Recent model guidance indicates precipitable water (PWAT) values near to slightly below normal, generally around 1.3 to 1.5 inches, while 700-500 mb relative humidity remains limited, promoting a stable pattern with a strengthening trade wind cap in place. As a result, expect mostly fair weather conditions, with only isolated, brief passing showers embedded within the trade wind flow, primarily affecting windward sectors during the early morning hours. During the afternoon, local effects and sea breeze convergence may lead to the development of isolated shallow showers over interior and western Puerto Rico, but rainfall accumulations should remain minimal.

By Tuesday and Wednesday, the pattern becomes slightly more dynamic as a polar trough and its associated frontal boundary approach from the western Atlantic. Although the boundary will remain north of the area, its proximity, combined with surface high pressure over the central Atlantic, will help maintain a southeasterly wind flow across the region. Aloft, this pattern will result in falling 250 mb heights and gradual cooling, leading to lower 500 mb temperatures and steeper 700-500 mb lapse rates, introducing a modest increase in instability. At the same time, PWAT values are forecast to increase slightly on Tuesday, with additional patches of low-level moisture advected into the area by Wednesday.

Despite these changes, moisture availability will remain the primary limiting factor, as mid-level drying persists and continues to restrict widespread deep convection. However, the combination of diurnal heating, local effects, and sea breeze convergence could support the development of isolated to scattered afternoon showers, particularly across the interior and northwestern portions of Puerto Rico on both days. Given the cooling aloft and above-normal low- level temperatures, isolated thunderstorms cannot be ruled out, although any activity is expected to be localized and short-lived. Hi-Res models continue to suggest limited overall coverage, reinforcing the expectation that convection will remain spotty rather than widespread.

Temperatures will remain above normal through the short-term period, supported by a warm airmass advected by southeasterly flow. This will promote heat indices reaching or slightly exceeding 100F, especially across coastal and urban areas, with a limited heat risk expected. This level of heat will primarily affect individuals who are particularly sensitive to heat, especially those outdoors without effective cooling and/or adequate hydration.

Long Term(Thursday through Monday)

Issued at 238 AM AST Mon May 4 2026

A transition toward a drier pattern is expected during the mid to late week period, particularly from around May 7 through May 10, as moisture decreases and subsidence strengthens across the region. This will lead to a noticeable reduction in shower activity and overall rainfall coverage. Temperatures will gradually rise under this pattern, supporting a limited heat risk, mainly affecting sensitive individuals exposed to prolonged outdoor conditions without adequate hydration or cooling.

Breezy conditions will continue, especially during the first half of the period, with easterly winds occasionally reaching locally fresh levels. This will result in a limited non-thunderstorm wind risk, with gusts around 20 to 25 mph possible at times, particularly across coastal and windward areas. While impacts remain minor, unsecured objects may be blown around, and these conditions could contribute to localized hazard enhancement when combined with drying conditions.

A secondary concern will be the potential for elevated fire danger. The combination of reduced rainfall, increasing temperatures, and breezy winds will promote the drying of fine fuels. In addition, Keetch-Byram Drought Index (KBDI) values exceeding 600 indicate increasingly dry soil conditions. These factors suggest that fire danger may increase across portions of the region, particularly across southern and windward coastal areas. Conditions will continue to be monitored for any further increase in fire weather risk.

AVIATION

(06Z TAFS) Issued at 238 AM AST Mon May 4 2026

Mainly VFR conds expected thru the fcst pd. FEW-SCT clouds at or above FL025 with limited SHRA activity. VCSH psbl ovr interior/wrn PR this aftn. ESE sfc winds at 10-15 kt with sea breeze variations and ocnl gusts up to 20 kt. The 04/00Z sndg shows winds up to 19 kt blo FL050. No sig avn impacts expected.

MARINE

Issued at 238 AM AST Mon May 4 2026

A broad high pressure over the central Atlantic will maintain an easterly flow over the next few days. Winds will remain generally gentle to moderate, around 10 to 15 knots, with a few periods of locally fresh conditions tonight into Monday. Seas will range between 3 and 5 feet, occasionally up to 6 feet due to a combination of local wind waves and a small, long-period northeasterly swell. Overall conditions will remain favorable for small craft, though operators should exercise caution at times due to wind-driven seas and passing showers that may produce locally higher winds and seas. A gradual improvement is expected later in the week as winds ease slightly and seas subside.

BEACH FORECAST

Issued at 238 AM AST Mon May 4 2026

A moderate risk of rip currents will continue across the north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through much of the workweek. A small, long-period northeasterly swell will occasionally promote higher breakers and stronger rip currents, particularly along the north-facing beaches of Puerto Rico. Conditions will gradually improve late in the week as the swell subsides, with a low risk of rip currents expected by Friday. While the overall risk will decrease, isolated stronger rip currents may still occur, and beachgoers should continue to exercise caution.

For additional information, visit weather.gov/beach/sju.

FIRE WEATHER

Issued at 238 AM AST Mon May 4 2026

Little to no rainfall is anticipated across the southern sections of Puerto Rico today. Drier air is also expected to filter into the region, allowing relative humidity values to drop into the upper 40s to low 50s. Wind speeds may reach around 16 to 21 mph, with higher gusts. KBDI values in Cabo Rojo remain above critical fire weather thresholds. Additionally, the 7-day percent of normal rainfall across the southeastern coastal plain, including areas near Salinas, is below 25%, with some locations even below 5%. Therefore, conditions will be favorable for the spread of wildfires along the southern coastal plains of Puerto Rico. A Fire Danger Statement (RFDSJU) has been issued.

SJU WATCHES/WARNINGS/ADVISORIES

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