Marine Weather and Tide Forecast for Luis M. Cintron, PR

SHORT TERM
Today through Monday...

Radar and satellite analysis indicated mostly quiet weather across Puerto Rico overnight, with areas of fog developing over the mountainous interior. Since 8 PM AST, scattered showers and isolated thunderstorms affected eastern Puerto Rico—including Vieques and Culebra—as well as the U.S. Virgin Islands, resulting in increased cloud cover and peak radar-estimated rainfall totals of 1 to 2 inches in Fajardo and Saint John. Winds were generally light, with measurable speeds below 10 mph mainly observed across windward coastal areas. Minimum temperatures dropped into the lower 60s in the higher elevations, while exposed coastal areas of southern and eastern Puerto Rico, along with the local islands, remained in the upper 70s.

A mid-to-upper-level cutoff low and its associated surface-induced trough will remain the dominant weather feature through the weekend.
This pattern will continue to support deep convective development, especially today and into early Sunday, aided by cooler-than-normal temperatures aloft and an abundance of tropical moisture. Precipitable water values today will range between 1.9 and 2.1 inches, near to above typical levels for this time of year. A gradual drying trend is anticipated beginning Sunday into early next week, as drier air filters in behind the upper-level trough. While winds will gradually diminish as the surface trough settles northeast of the region over the next few days, breezy conditions may persist today around the Anegada Passage, just east of the U.S. Virgin Islands.

Despite the presence of a Saharan Air Layer (SAL), which may locally suppress convective activity, today is still expected to be the most active day of the short-term period. Scattered to locally numerous showers and isolated thunderstorms are forecast, with the greatest impacts likely over eastern Puerto Rico, the Cordillera Central, and northwestern Puerto Rico, including the San Juan metro area. Rains from slow-moving showers will support a limited to elevated risk of excessive rainfall. The strongest thunderstorms may also produce frequent lightning, strong wind gusts, and the potential for small hail. Given already saturated soils, urban and small stream flooding, localized flash flooding, and landslides remain possible.

The overall pattern becomes less favorable for organized convection by Sunday and Monday. While isolated to scattered showers and thunderstorms will still be possible, mainly during the afternoon hours, activity is expected to be less frequent and less intense, with flooding threats becoming more localized. Temperatures will remain near seasonal normals throughout the period, though a limited excessive heat hazard may develop across northern and western Puerto Rico on Sunday and Monday. Please refer to the Experimental Graphical Hazardous Weather Outlook for the latest depiction of at- risk areas.

LONG TERM
Tuesday through Saturday...

The forecast remains generally on track for the long-term period.
At the surface, a high-pressure system over the Atlantic Basin will maintain an easterly to southeasterly wind flow throughout the forecast period. On Tuesday and Wednesday, a weak upper-level trough will move across the area, while a mid-level ridge builds over the western Caribbean. Winds will remain light through at least midweek, then gradually increase from Thursday onward. According to the latest model guidance, precipitable water values will fluctuate around seasonal averages—approximately 1.8 inches on Tuesday, decreasing to between 1.5 and 1.7 inches on Wednesday and Thursday, and rising again to around 1.8 inches by Friday afternoon onward.

Given this pattern, marginally unstable conditions are expected mainly on Tuesday and Wednesday. The combination of moisture, daytime heating, and local effects will favor shower development, particularly during the afternoon hours. However, the likelihood of thunderstorms will decrease as 500 mb temperatures rise into an above-average range (around -4 to -5 degrees Celsius), which could limit convective development. On the other hand, by the end of the week, temperatures are forecast to return to around -7 degrees Celsius at 500 mb, increasing the potential for thunderstorm activity with afternoon convection, but less moisture and instability will be available. From Thursday through Saturday, the upper- level trough will shift to our east, placing its convergent side over the region, while the mid-level ridge shifts eastward and exerts more influence, promoting more stable atmospheric conditions.
Either way, afternoon convection cannot be ruled out due to the available moisture (mainly confined in the lower levels of the atmosphere) and local effects, particularly across the western portion of Puerto Rico during peak heating hours.

Temperatures are expected to remain warmer than normal throughout the forecast period, as suggested by 925 mb temperatures, which will peak on Tuesday and stay above average for the rest of the week.
Also, model are still showing Saharan dust concentrations over the region at least through Tuesday.

The main takeaway is that there will likely be rainfall activity each day, mainly during the morning in eastern Puerto Rico and the U.S. Virgin Islands, and during the afternoon in western Puerto Rico. Tuesday has the highest probability of afternoon rainfall in the west, with chances between 60% and 70%, followed by Wednesday with 50% to 60%. From Thursday through Saturday, more stable conditions are expected, but available moisture should still result in afternoon convection, although it is not expected to be deep or widespread. The flood risk will likely remain limited.

AVIATION
(06Z TAFs)

Unsettled conditions will bring MVFR and brief IFR periods at most TAF sites, continuing across USVI terminals through the period.
SHRA/TSRA will affect Puerto Rico terminals mainly between 17/16- 22Z. Saharan dust concentrations remain minor, with visibility above 6 miles, except near +SHRA/TSRA. Light to calm winds at first, increasing to 8–12 mph with strong sea breeze variations after 17/14Z. Gusts possible near strong TSRA.

MARINE

A surface trough will influence light to moderate easterly winds. A deep trough with its axis currently located to the west of the region will continue to support unsettled weather conditions today, with a high chance of thunderstorm development mainly across the eastern local waters. These storms could lead to locally higher winds and seas. In addition, hazy conditions are likely over the next few days due to the presence of Saharan dust.

BEACH FORECAST

There is a low rip current risk today across all coastal areas of the islands as winds are expected to become lighter. However, life-threatening rip currents often occur near groins, jetties, reefs, and piers. Similar conditions are expected to prevail over the weekend and into early next week. A moderate rip current risk will likely return around midweek. For more information, please refer to the latest Coastal Hazard Message (CFWSJU) and Surf Zone Forecast (SRFSJU).

HYDROLOGY

Abundant tropical moisture (with heavy moisture levels) and increased instability due to a nearby cutoff low will keep the flood risk high across Puerto Rico and the U.S. Virgin Islands today and tonight. Since soils are already saturated and some rivers are running high, any additional heavy rain could cause urban and flash flooding, river flooding, and landslides—even after the heaviest rain stops. For more details, please see the Hydrologic Outlook (ESFSJU).

SJU WATCHES/WARNINGS/ADVISORIES
PR...None.
VI...None.
AM...None.