textproduct: San Juan

KEY MESSAGES

Issued at 155 PM AST Wed Nov 4 2026

- A light and moist south-southwesterly wind flow will bring increasing showers and thunderstorms across the area for the next several days, particularly affecting the interior, northeast and the San Juan metro area. Urban and small stream flooding is anticipated, while isolated flash flood cannot be ruled out.

- Passing showers are also expected for the Virgin Islands, but the risk of flooding is limited.

- Another northerly swell is expected this weekend, increasing the rip current risk to high for northern Puerto Rico, Culebra, and St. Thomas.

Short Term(This evening through Friday)

Issued at 155 PM AST Wed Nov 4 2026

Afternoon convection forming over the Cordillera Central will gradually taper off in the early evening hours. Some of these showers will move toward the local waters in the Caribbean and the vicinity of the Virgin Islands. Otherwise, the night should be mild with temperatures dropping to the low 80s or mid and upper 70s.

A trough over the western Caribbean and a high near the Lesser Antilles will maintain a weak pressure gradient, causing light winds coming from the south-southeast. As an upper-level ridge begins to lose influence of the local islands, conditions aloft will become more favorable for shower formation. The first round of showers is expected in the afternoon, but because the winds are from the southwest, the focus of rain should be across the central interior, east interior, and the San Juan metro area. Light winds may contribute in higher rainfall accumulations, likely causing urban and small stream flooding, while isolated flash flooding cannot be ruled out. On Thursday night, moisture will further increase, with values much above the climatological value for this time of year. Therefore, showers will reach the coastal areas of western and southern Puerto Rico, while additional showers will reach portions of the Virgin Islands. The users are advised to maintain situational awareness during the night hours, especially for those living near creeks and flood prone areas.

The unsettled weather pattern is expected to persist into Friday. In fact, the GFS forecast sounding exhibit some characteristics of favorable conditions for flooding, like a skinny shape (temperature and dew point close together) and moderate values of CAPE, although average wind shear is strong in the surface to 3 km layer. All of this translate into a medium to high confidence of experiencing at least some degree of flooding, especially if the terrain gets saturated with the rain observed today and on Thursday. Again, the area that will likely receive the heaviest rain will be the east- interior, northeast, and the San Juan metro area.

Additional threats associated with this week's rainfall include frequent lightning. Also, 925 mb temperatures remain nearly two standard deviation above normal, Thus, before the onset of the rain, heat indices will be elevated, impacting mostly those very sensitive to heat, especially if outdoor or without adequate hydration.

Long Term(Saturday through Tuesday)

Issued at 200 AM AST Wed Nov 4 2026

Following the trend of the short term period, by Saturday, atmospheric instability and available moisture will remain elevated. Precipitable water (PWAT) will continue generally above normal (2 inches) as a southwesterly steering flow continues to bring tropical moisture towards the islands. This tropical moisture will continue to move northwards and upper-level trough and its corresponding frontal low. Although the core of maximum instability is still forecast to pass north of the area, this pattern will continue to result in a generally WSW to W surface flow to start the period. 925 mb winds will increase to more seasonal levels on Saturday before decreasing to more light and variable Sunday through at least early Wednesday. Relative humidity from 850 to 700 mb and from 700 to 500 mb should remain at high end normal to above normal values for the month on Saturday. Showers and t-storms are likely to develop to start the period, generating elevated rainfall totals, primarily across the southern, interior, northern and northeastern sectors of Puerto Rico, as well as the U.S. Virgin Islands. This will result in flooding (Risk level 2 of 4) especially across interior, northern and northeastern Puerto Rico during the afternoon hours with these showers and t-storms possibly moving east towards Vieques, Culebra and the northern USVI.

With the upper trough and frontal low moving away from the area, a transition to a more stable pattern with mid-to-upper level riding is forecast Sunday through Wednesday. Models are in more agreement in terms of moisture availability than in the past few days. PWAT and RH values are forecast to fluctuate between normal to above normal values during that period, with a sharper decrease towards more normal values Tuesday into Wednesday. As mentioned above, 925 mb wind speeds will be on a decreasing trend Sunday onwards before gradually increasing once again towards Wednesday. These lighter and variable surface winds will gradually pick up from the ESE and then E to end the period, albeit under a more southerly steering flow. Although daytime heating and localized effects may still generate scattered afternoon convection across the islands, a general decrease in shower activity and intensity is expected when compared to the short term period and Saturday, reducing the flood threat. 925 mb wind speeds are still forecast at above normal values for most of the period. Please stay tuned for subsequent updates as the forecast evolves.

AVIATION

(18Z TAFS) Issued at 155 PM AST Wed Nov 4 2026

VFR conds should persist across all TAF sites, though aftn - TSRA/+TSRA will reduce CIGs/VIS, with TEMPO MVFR conds through 04/20z; VCTS could be expected across the USVI TAFs in the evening. Weak SW-W winds btwn 5 - 10 kt will cont this aftn, becoming light and VRB by 04/23z, picking up btwn 5 - 10 kt once again by 05/12- 14z. Low concentrations of HZ may slgty reduce VIS, but should remain above 6SM.

MARINE

Issued at 155 PM AST Wed Nov 4 2026

A developing low pressure north of Puerto Rico will continue to weaken the local pressure gradient today, resulting in generally light southwesterly winds for the next few days, becoming variable from time to time. Showers and thunderstorms will increase across the regional waters, particularly Thursday and Friday, producing locally gusty winds, reduced visibility, and lightning. Seas will continue to subside before a north-northwesterly swell arrives Friday and builds through the weekend, leading to hazardous conditions for small craft across the Atlantic waters and exposed passages. Pulses of a northeasterly swell may arrive early next week.

BEACH FORECAST

Issued at 155 PM AST Wed Nov 4 2026

The beach forecast remains on track. Northern and eastern-exposed beaches of the islands continue under a moderate risk of rip currents, while the low risk continues elsewhere. Beachgoers must exercise caution, as life-threatening rip currents remain possible along the surf zone. As mentioned in previous discussions, the risk may downgrade at most beaches of the islands tonight and Thursday, however, the arrival of a long-period north-northwesterly swell on Friday, increasing the rip current risk. Therefore, a high rip current risk is likely across northern-exposed beaches Puerto Rico and the U.S. Virgin Islands on Saturday and Sunday. The risk may persist early next week, as pulses of another swell may reach the regional waters. Besides rip currents, beachgoers should continue to monitor weather conditions, as shower and thunderstorm activity may move across coastal areas of northeastern and eastern Puerto Rico, including the San Juan Metropolitan area. Periods of heavy rainfall, gusty winds, and lightning are very likely; seek shelter whenever you hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>013.

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

AM...None.