Marine Weather and Tide Forecast for Catano, PR

SHORT TERM
Tonight through Wednesday...

Once again, the presence of a thick upper-level cloud deck over the islands delayed the onset of afternoon showers. However, the Doppler radar detected a streamer downwind from the northern USVI and Culebra, spreading into the northeast PR and affecting the San Juan Metro area. Sea breezes developed, producing convection across western Puerto Rico. Maximum temperatures ranged from the upper 80s to the low 90s, with heat indices reaching around 103 degrees Fahrenheit due to the available moisture, primarily at urban and coastal sites.

Showers and thunderstorms may result in flooding rains through this evening, mainly across the west municipalities of PR. The lingering Saharan Air Layer will produce hazy skies through at least the middle of the week. This air mass will limit nighttime cooling, promoting warmer-than-normal minimum temperatures across Puerto Rico and the US Virgin Islands.

No significant changes were introduced to this afternoon's forecast as it continues on track. Thus, from Monday night through Wednesday, the local area will be positioned between a westward- moving upper-level low and a developing cut-off low to the northeast, resulting in an upper-level omega-like pattern with weak ridging aloft. This setup will enhance upper-level stability by Wednesday and lead to a notable drying trend, with precipitable water values dropping from around 2.10 inches to 1.40 inches and mid-level relative humidity decreasing significantly. As moisture availability declines, shower activity will follow a typical diurnal pattern with reduced coverage. While localized afternoon thunderstorms may still develop, the overall flooding threat will be limited to elevated levels during peak heating hours.

LONG TERM
Thursday through Monday
from prev discussion

Variable conditions are expected for the long-term forecast.
Easterly-southeasterly winds will dominate most of the period due to a surface high pressure over the western Atlantic. Based on the latest global guidance, Precipitable Water values will gradually increase by the end of the workweek due to a tropical wave currently located over the eastern Atlantic. By Friday into Saturday, moisture associated to the tropical wave is expected to pool over the region, but suspended Saharan dust lingering over the region may suppress significant shower activity over the local area. The presence of a mid- level ridge over the CWA should limit deeper convection activity during that period as well, with warmer 500 mb temperatures (around -5 Celsius). Sunday may also be the "driest" day of the long- term, based on recent guidance, with PWAT value decreasing to below normals (around 1.4 inches), with RH values in the low to mid levels plummeting to 10%.
Although deeper convection activity may be limited, the combination of diurnal heating, sea breeze convergence, and local effects could enhance shallow convection over western/northwestern PR each afternoon. Another tropical wave should approach the local islands by Sunday night into Monday, pooling well above normal moisture (2.0 - 2.2 inches). Temperatures in the 500 mb layer should cool to seasonal to near below normals (- 7 to - 8 Celsius), supporting deep convection activity. The frequency of showers and thunderstorms should increase across the CWA, but there's uncertainty due variations in previous model cycles.

Under an E-SE wind flow with abundant moisture, heat indexes are likely to exceed 100 degrees Fahrenheit each day, mainly over urban and coastal areas of Puerto Rico. Hence, the risk will remain limited, affecting individuals sensitive to heat.

AVIATION
Expect mostly VFR conditions at all TAF sites during the period, although hazy skies will persist due to SAL. VCTS will develop near JBQ, and some SHRA/+SHRA will impact JSJ through 16/23z.
SHRA/TSRA will expand across the surrounding waters and may impact local terminals, especially JSJ/IST/ISX, after 16/22z into tomorrow. E-SE 15-20 knots with local sea breezes accompanied by higher gusts. Winds bcmg less than 10 kts aft 16/23Z, and returning to similar wind conditions as today after 13/13z tomorrow.

MARINE

The surface high pressure northeast of the region will continue to gradually shift east over the coming days. While some fluctuations in the wind pattern are expected, moderate to locally fresh winds from the east to east-southeast will promote choppy conditions mainly over exposed areas, small craft should exercise caution. A plume of suspended Saharan dust is expected to linger through midweek, potentially causing a slight reduction in visibility. Meanwhile, increasing moisture and instability associated with an upper-level trough will likely lead to a rise in thunderstorm activity into early in the week.

BEACH FORECAST

Breezy to locally windy easterlies will maintain a moderate risk of rip currents for most beaches of Puerto Rico and the US Virgin Islands. Beachgoers must exercise caution due to life-threatening rip currents along exposed unprotected beaches. Additionally, please be advised of the possibility of seeing afternoon thunderstorms, particularly over western and northwestern Puerto Rico.

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