Major SoCal late August heatwave this week, with modest but growing possibility of tropical storm remnants affecting CA in September

Key Points:

• The American West is experiencing a record warm summer with notably elevated overnight temperatures, especially in inland and southern California, driven by warm ocean waters and persistent drought conditions; daytime temperatures have been closer to average, explaining why the heat may feel less intense.
• Southern California and southern Arizona face a potentially extreme heatwave this week due to a strong atmospheric ridge, with inland valleys possibly reaching near or above 110°F; elevated coastal humidity will increase heat stress and overnight temperatures, and there is a 30-40% chance of intensified heat from offshore winds that could also raise wildfire risks.
• There is a modest but increasing probability (5-20%) of a tropical storm or depression bringing remnant moisture to California in early September, linked to warm Pacific waters and reduced wind shear from El Niño, warranting close monitoring during peak tropical season.
• Recent research highlights that Western U.S. snowpack has declined by about 25% since the 1980s, but year-to-year variability has increased significantly (44% in variability, 80% in intensity), with more extreme low snow years but no reduction in high snow years, suggesting greater "snowpack whiplash" likely influenced by climate change.
• El Niño is already strong and expected to peak between October and December at historic levels, likely causing major global temperature and precipitation impacts; California can expect wetter-than-average conditions in late 2026 with increased risks of flooding and coastal hazards, while the hottest year on record globally is anticipated in 2027.