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Nerd mode: every forecast, readouts, filters and range & bearing for weather enthusiasts

This week’s weatherSan Juan, PR

Rain is likely in San Juan on Monday

7 in 10 of NOAA’s 31 GEFS forecasts bring measurable rain to San Juan Mon 8 p.m.–2 a.m. AST.

NOAA GEFS, 31 forecasts · Mon 28 Sep 18Z run · updated Mon., Sept. 28, 7:03 p.m. AST · times are San Juan’s (AST)

See it on the globe Official National Weather Service forecast

Quick answers

Will it rain in San Juan this week?
The best chances of measurable rain: Monday (7 in 10 forecasts, 8 p.m.–2 a.m.); Tuesday (8 in 10 forecasts, 8 a.m.–2 p.m.); Wednesday (nearly all forecasts, 8 p.m.–2 a.m.); Thursday (8 in 10 forecasts, 2–8 a.m.). Times are AST.
How much rain will San Juan get this week?
By Mon., Oct. 5, 2 p.m. AST (the end of the forecast), the middle forecast has 0.55 in of rain and melted snow, counting from Mon 8 p.m. 6 in 10 forecasts bring 0.5 in or more in total.
How windy will it get in San Juan?
No strong gusts: fewer than 1 in 10 forecasts have gusts over 30 mph at any of the six-hourly times. The middle forecast’s strongest gust is 17 mph, Wed 2 p.m. Checked every six hours, so a brief peak can fall between.
How warm or cold will it be in San Juan?
At the six-hourly times, the middle forecast runs from 78°F (Sat 2 a.m.) to 84°F (Tue 2 p.m.) AST. The day’s real high and low can fall between those times.
Are any storms heading for San Juan?
No storm Stormlines tracks has 1 in 10 forecasts passing its centre within 100 miles of San Juan this week.

Chance of rain, six hours at a time

Mon 8 p.m.–2 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inTue 2–8 a.m.: fewer than 1 in 10 forecasts with measurable rain; middle forecast almost noneTue 8 a.m.–2 p.m.: 8 in 10 forecasts with measurable rain; middle forecast 0.02 inTue 2–8 p.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inTue 8 p.m.–2 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inWed 2–8 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inWed 8 a.m.–2 p.m.: 8 in 10 forecasts with measurable rain; middle forecast 0.02 inWed 2–8 p.m.: 8 in 10 forecasts with measurable rain; middle forecast 0.02 inWed 8 p.m.–2 a.m.: nearly all forecasts with measurable rain; middle forecast 0.03 inThu 2–8 a.m.: 8 in 10 forecasts with measurable rain; middle forecast 0.02 inThu 8 a.m.–2 p.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inThu 2–8 p.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inThu 8 p.m.–2 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inFri 2–8 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inFri 8 a.m.–2 p.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.02 inFri 2–8 p.m.: 8 in 10 forecasts with measurable rain; middle forecast 0.02 inFri 8 p.m.–2 a.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.02 inSat 2–8 a.m.: 5 in 10 forecasts with measurable rain; middle forecast 0.01 inSat 8 a.m.–2 p.m.: 5 in 10 forecasts with measurable rain; middle forecast almost noneSat 2–8 p.m.: 7 in 10 forecasts with measurable rain; middle forecast 0.01 inSat 8 p.m.–2 a.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.01 inSun 2–8 a.m.: 5 in 10 forecasts with measurable rain; middle forecast 0.01 inSun 8 a.m.–2 p.m.: 5 in 10 forecasts with measurable rain; middle forecast 0.01 inSun 2–8 p.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.01 inSun 8 p.m.–2 a.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.01 inMon 2–8 a.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.01 inMon 8 a.m.–2 p.m.: 6 in 10 forecasts with measurable rain; middle forecast 0.01 in

Each bar is the share of the 31 forecasts with measurable rain or melted snow in that six hours; the darker the bar, the more forecasts agree. Local days, AST.

The week, day by day

DayChance of rainA tenth of an inch or moreTotal by day’s endStrongest gustTemperature
Mon 28 (rest of day)7 in 10<1 in 100.02 in · <1 in 1013 mph80°F
Tue 298 in 10<1 in 100.08 in · <1 in 1016 mph79°F–84°F
Wed 30nearly all<1 in 100.19 in · <1 in 1017 mph79°F–84°F
Thu 18 in 10<1 in 100.27 in · <1 in 1016 mph79°F–84°F
Fri 28 in 101 in 100.36 in · 1 in 1016 mph79°F–84°F
Sat 37 in 101 in 100.43 in · 4 in 1015 mph78°F–84°F
Sun 46 in 101 in 100.52 in · 5 in 1015 mph79°F–84°F
Mon 5 (part)6 in 10<1 in 100.55 in · 6 in 1013 mph79°F–84°F

Chances are the highest in any six hours of the day. “Total by day’s end” is the middle forecast’s running total since Mon 8 p.m., and the share of forecasts with 0.5 in or more by then; totals aren’t added up day by day, because the middle forecast of each day isn’t the same forecast. Gusts and temperatures are read every six hours.

Storms near San Juan

No storm Stormlines tracks has 1 in 10 forecasts passing its centre near San Juan this week. Every storm we’re tracking →

About these numbers

They come from one source, NOAA’s Global Ensemble Forecast System (GEFS): 31 runs of the same model, each started slightly differently, read at San Juan’s coordinates on a grid about 55 km (35 miles) apart. “8 in 10 forecasts” means 8 in 10 of those runs. Nothing is adjusted for local effects such as coasts, lakes, hills or city heat, so the numbers can differ from your local official forecast, especially for snow and showers.

“Measurable rain” counts rain or melted snow in a six-hour period. Not an official forecast: see the National Weather Service forecast for warnings and decisions. How the forecasts are read: how to read the maps and the glossary.

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