Monsoonal Rain, Thunderstorms Sweep Into Southland on Thursday, Friday

Showers and thunderstorms are expected across Southern California Thursday and Friday, prompting a flood watch for many areas.

The region is in the grip of a muggy heat wave that will yield to monsoonal moisture early Thursday, according to the National Weather Service. Temperatures will drop significantly from Wednesday’s highs, but humidity will remain elevated, as high as 69% in Los Angeles County, forecasters said.

Pasadena’s daytime highs were expected to reach 84 degrees, with overnight lows near 66.

Thursday morning began with humid skies and scattered showers. Temperatures hovered near 69 degrees, with light east-northeast winds around 5 mph and mostly cloudy conditions.

The chance of precipitation Thursday is 90 percent. Rainfall amounts could reach up to half an inch in areas affected by thunderstorms. Winds were forecast to shift to southerly by afternoon, increasing to 10 mph.

Friday’s forecast includes a 50 percent chance of showers and thunderstorms, mainly in the morning. Skies will gradually clear, with highs near 82 degrees and light, variable winds. Friday night will be mostly clear with lows around 61.

Weekend conditions are expected to be dry and sunny. Highs will remain in the low to mid-80s, with overnight lows steady near 61 degrees. Humidity will persist.

Rainfall totals will vary widely. Most areas will receive less than a quarter inch, though isolated locations may see up to 0.40 inch. A slight chance of showers returns Monday and Tuesday.

Winds will remain light throughout the forecast period. Breezes will shift from east-northeast to southerly Thursday, then calm overnight. Friday and Saturday will feature light south-southeast and southwest winds.

Localized flooding is possible, especially in foothill areas and near recent burn scars. Pasadena’s Department of Public Works advised residents to avoid flood-prone intersections and secure outdoor items.

The Flood Watch issued by the National Weather Service remains in effect through early Friday morning. Residents are urged to monitor updates and avoid travel during heavy rainfall.

Next week begins with a slight chance of showers Monday and Tuesday. Dry and warmer conditions are expected to return by Wednesday, with highs near 87 degrees.

Pasadena faces a brief but intense tropical weather pattern through Friday. A sunny weekend will bring relief, though humidity and slight rain chances may return early next week.

Here is the latest forecast for Pasadena from the National Weather Service as of 5:19 a.m. Thursday:

Overnight: Showers and possibly a thunderstorm. Low around 69. East northeast wind around 5 mph. Chance of precipitation is 90%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Thursday: Showers and possibly a thunderstorm. High near 84. East northeast wind 5 to 10 mph becoming south in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Thursday Night: A 40 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 66. South southeast wind 5 to 10 mph. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Friday: A 50 percent chance of showers and thunderstorms. Mostly cloudy, then gradually becoming sunny, with a high near 82. South southeast wind around 5 mph becoming calm. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Friday Night: Mostly clear, with a low around 61. Southwest wind around 5 mph becoming calm in the evening.

Saturday: Sunny, with a high near 84.

Saturday Night: Mostly clear, with a low around 61.

Sunday: Sunny, with a high near 83.

Sunday Night: Mostly clear, with a low around 61.

Monday: A slight chance of showers after 11:00 a.m. Mostly sunny, with a high near 87.

Monday Night: A slight chance of showers. Mostly clear, with a low around 65.

Tuesday: A slight chance of showers. Sunny, with a high near 87.

Tuesday Night: Clear, with a low around 63.

Wednesday: Sunny, with a high near 87.