Marine Weather and Tide Forecast for Jobos, PR

SHORT TERM
Today through Saturday...

Calm weather conditions prevailed overnight, with land breezes observed in most coastal areas. Overnight minimum temperatures dropped to the mid to upper 70s along the coast and to around the mid-60s in the mountains.

Another above-normal temperature day is expected today, although to a lesser extent than in recent days. The 22/06Z 925 mb temperature data from NUCAPS showed values ranging from 20.7C to 21.7C across the forecast area, about 1 to 2 degrees Celsius higher than what model guidance indicated for that time. A similar pattern was noted in the 22/00Z TJSJ upper-air sounding, which showed 925 mb temperatures about 1 degree warmer than model forecasts. All observed values remain well above the climatological normal for this time of year. Moisture levels will be slightly lower compared to recent days, which may lessen the impact on heat index values.
However, with the warming trend persisting and sufficient moisture still present, a Heat Advisory has been issued, this time limited to the northern and western municipalities of Puerto Rico. Residents are advised to limit strenuous outdoor activities to the early morning or evening hours and to stay well-hydrated throughout the day. A gradual decrease in temperatures is expected over the coming days.

Today and through the short-term forecast period, a slight shift in the weather pattern is expected. The upper-level trough that has been influencing the northeastern Caribbean will continue to move eastward. In its wake, weak ridging aloft will build over the forecast area, accompanied by a gradual increase in 250 mb heights.
However, marginal instability will persist, especially today, as the upper-level trough remains nearby. Instability indicators, such as 500 mb temperatures and low- to mid-level lapse rates, will remain at near normal levels.

As mentioned earlier, a slightly drier slot, as observed by GOES-19 Precipitable Water satellite data, is expected to move in during the morning hours. However, an east-southeast wind flow will help return moisture levels to near normal by this afternoon, with those conditions expected to persist through the rest of the short-term period. Steering winds will strengthen today as a surface high pressure over the central Atlantic builds, increasing the pressure gradient over the northern Caribbean through the weekend. Shower and thunderstorm activity will follow a typical seasonal pattern, with some showers developing over local waters during the night and early morning, occasionally moving over windward coastal areas.

During the afternoon, marginal instability combined with sufficient moisture, surface heating, sea breeze convergence, and orographic lifting will support the development of showers and isolated thunderstorms over the interior and western portions of Puerto Rico.
The highest rainfall accumulations are expected this afternoon, as today will feature the greatest instability due to the proximity of the upper-level trough and slower steering winds. This could lead to an elevated flooding risk in very localized areas out west. On Friday and Saturday, rainfall accumulations during the afternoon are expected to decrease due to faster-moving showers and the trough shifting farther away. Nonetheless, a limited flooding risk will still be present.

LONG TERM
Sunday through Thursday...

The long-term forecast remains on track, with a variable pattern ahead. Another surface high pressure in the western Atlantic is likely to migrate eastward and build over Central Atlantic, promoting easterly trades through most of the period. The weather conditions for early next week will most likely be seasonal, with Precipitable Water (PWAT) values around 1.7 - 1.8 inches and 500 mb temperatures between -7.5 and -8.0 Celsius. With increasing winds, deep convection activity is expected to develop in the afternoon mainly over portions of western Puerto Rico. Streamers created by the local islands may also move into portions of eastern Puerto Rico as well.

The deep upper-level trough northwest of the CWA is still expected to approach the local area by Monday into Tuesday. Additionally, a tropical wave located at approximately 32W is also anticipated to approach the forecast area now on Monday evening into Tuesday. Based on deterministic guidance from the GFS and ECMWF, the combination of moisture associated to the tropical wave and the upper-level trough will increase PWAT values to above climatological normal.
Additionally, colder 500 mb temperatures will enhance deep convection activity. Hence, moderate to locally heavy rainfall and thunderstorms mainly over the windward sections during the night and early morning and into western portions of Puerto Rico in the afternoon. The flooding potential will remain elevated for the aforementioned areas.

Ensemble members agree that a less wet pattern for the second part of the workweek is the most likely scenario due to the approach of a Saharan Dust layer. From the latest guidance, the highest concentrations should remain south of the region, but uncertainty remains high. Under that scenario, deep convection activity should remain limited with isolated thunderstorms in the afternoon. However, the combination of daytime heating, local effects, and available moisture may trigger showers in the early morning over windward sections and western/northwestern Puerto Rico in the afternoons.

By Thursday, decreasing winds from the southeast will pool warmer and humid air into the local area. This is also reflected in the 925 mb temperatures, which will increase to above climatological normal again. Hence, a limited risk of excessive heat is likely and may affect most individuals sensitive to heat.

AVIATION
(06Z TAFs)

Mainly VFR conditions will prevail across most terminals. Afternoon SHRA/TSRA could cause mtn top obsc and brief MVFR/IFR at TJBQ between 22/17-22Z. Calm to light and variable winds becoming more easterly with sea breeze variations at 10-15 mph aft 22/14Z. Winds become light and variable aft 22/22Z.

MARINE

A building surface high pressure over the central Atlantic will promote gentle to moderate easterly trades today, becoming moderate to locally fresh by Friday. Isolated thunderstorms will continue to develop across the regional waters, particularly across the northern and western coastal waters of Puerto Rico each afternoon.

BEACH FORECAST

The risk for rip currents will remain low today for all beaches and coastal areas of the local islands. However, gradual increase of winds will most likely promote a moderate risk of rip currents by tomorrow Friday into the weekend. Beachgoers must exercise caution.

SJU WATCHES/WARNINGS/ADVISORIES
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for PRZ001-005-008-010.

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