Wednesday, September22, 2021
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Marine Weather and Tides
Arroyo, PR

Version 3.4
3/30/2021 -- ANZ330 has been split into ANZ331 and ANZ332. Click EDIT in Marine Forecast and select your new zone.
1/26/2021 -- The West Coast Satellite images havd been updated. They now use GEOS-17.
1/1/2021 -- The 7 day forecast are now working well. Thank you NOAA for your support.

Sunrise 5:28AMSunset 5:37PM Wednesday September 22, 2021 8:13 PM CST (02:13 UTC) Moonrise 8:33PMMoonset 7:45AM Illumination 97% Phase: Waning Gibbous; Moon at 16 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Arroyo, PR
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location: -34.81, -58.22     debug

Area Discussion for - San Juan, PR
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Area Forecast Discussion National Weather Service San Juan PR 942 PM AST Wed Sep 22 2021

UPDATE. Fair weather has prevailed across the local area, and only very isolated showers over the waters have been observed. It was relatively hot across northern PR, and the temperature reached 96 degrees for a brief moment at the San Juan International Airport, breaking today's record. This general pattern is expected to continue overnight as a drier than normal air mass persists over the local area tonight and tomorrow. The wind is still expected to remain southerly but light.

AVIATION. VFR conds expected through the forecast period. No rain is expected overnight and most of tomorrow. Winds will be light and southerly tonight, but could be variable at times. The southerly winds will continue after 23/13Z and may increase slightly to 10kt, but will have sea breeze variations at TJSJ and TJBQ.

MARINE. Tranquil seas up to 4 feet and winds up to 15 knots expected tonight into Thursday. There is a low risk of rip currents tonight across the local beaches, except for northern PR, which will have a moderate risk.

PREV DISCUSSION. /issued 453 PM AST Wed Sep 22 2021/


Drier, less active weather will continue into the end of the week, as will warmer than average temperatures. Moisture is expected to arrive late Friday into Saturday, which will bring an increase in shower activity.

SHORT TERM . Tonight through Friday .

Drier air has made its way into the region today, which has led to a marked decrease in shower activity. Based on satellite estimates, precipitable water values are now below normal values, around 1.3 to 1.5 inches, across the area. Southerly winds persist tonight; any showers that push onshore will likely do so in southern/southeastern Puerto Rico, and possibly windward portions of the other local islands.

Below normal moisture will persist through Thursday, inhibiting shower activity. Even so, some afternoon convection is anticipated for northern and interior Puerto Rico, due to local effects and daytime heating.

Some moisture will begin to push into the region from the east during the day on Friday. Winds are forecast to back tomorrow night into Friday morning to be from out of the southeast to east- southeast. With the additional moisture, an increase in shower activity is likely, with the bulk of the showers occurring in northwestern and interior portions of Puerto Rico.

Temperatures are likely to be somewhat above normal into the end of the week, under the influence of decreased shower activity and southerly winds.

LONG TERM . Saturday through Wednesday . From Prev Discussion .

Some discrepancies exist at upper levels with global models agreeing on the existence of a ridge at 500 mb, but diverging some on the passage of weak short upper level troughs across the area. The GFS for now is showing moistening at mid to upper levels between Saturday afternoon through Sunday morning with slightly steeper 700-500mb lapse rates compared to the ECMWF model. Although ECMWF shows moist low levels, the model exhibits much drier air aloft during this period with relative humidities remaining at or below 40%. Despite these small discrepancies, a fairly seasonal weather pattern can be expected this weekend through early next week with near normal to normal moisture content at low levels under east southeasterly trades. Under this pattern and marginal instability, passing showers will mainly affect the eastern coast of Puerto Rico, Vieques and Culebra as well as across the U.S. Virgin Islands each morning. In the afternoons, due to a combination of diurnal heating, available moisture and sea breeze convergence, showers and isolated thunderstorms can be expected to shift to the interior and western sections of Puerto Rico. Locally induced effects could also produce streamers and rainfall activity downwind of the Luquillo Mountain Range and the local islands producing scattered showers and isolated thunderstorms mainly during afternoon hours. Urban and small stream flooding can be expected in areas with the heaviest showers.

Attention will turn to a vigorous tropical wave (Invest 98L), currently located across 30 degrees west longitude as of this morning, as some of the model guidance bring this feature close to the local area by mid week. Disagreement lies in the path and intensity of Invest 98L with the National Hurricane Center designating a 90% of formation chance through 5 days. The GFS model is more bullish with the intensity but the latest run adjusted the path further northeast of the forecast area. ECMWF model, on the other hand, is far weaker and slower with 98L but puts it on a closer path to the region. Therefore, confidence continues to remain low on how significant of an impact 98L will have on the forecast area. At this point, it is best to continue monitoring the latest forecast updates throughout the rest of the week as model consensus improves.


Mainly VFR conditions are expected to prevail during the next 24 hours across all termimals. However, showers with possible isolated thunderstorms may develop in and around TJSJ this afternoon. VCTS at TJBQ thru 22z, mainly for offshore TSRA. Light southerly winds expected to continue through Wednesday.


Conditions have improved across the offshore Atlantic waters, and seas are expected to remain generally 4 feet or less across the local waters overnight tonight. A slight increase in wave heights is possible late tomorrow/tomorrow night, associated with a weak northerly swell that is forecast to make its way into the region. Even so, seas of 5 feet or less are anticipated. There remains southerly winds over the area, up to 15 knots, becoming more southeasterly tomorrow into Friday.

Tonight and tomorrow, there is a moderate risk of rip currents for some northern beaches of Puerto Rico and Culebra.

PRELIMINARY POINT TEMPS/POPS. SJU 78 92 78 92 / 20 20 10 30 STT 79 88 80 88 / 20 10 30 30



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