Cooler Climate Pattern Change for California Discussion: Due to tropical cyclone activity up-welling cooler subsurface water a large area of ocean surface west-southwest of Baja California has cooled the past couple weeks (Fig. 1). The cooler SSTA in this region identifies the first cooler-than-normal since late summer 2013. Interestingly, mid-summer was hot in California in 2013 reversing somewhat cooler in AUG/SEP. The cooler ocean surface change was caused by tropical cyclone activity rather than a large-scale climate pattern change so there is questions on how long this cool pattern will last. However, the short-term (next 4 weeks – at least) implications are a climate pattern across California defeating any anomalous heat risk. Model forecasts from last week indicated one more potential extreme heat event in the Los Angeles basin for MON-WED of this week. The forecast has been revised much cooler. Previously, an amplified ridge pattern northeast of Hurricane Lane was projected to give the Los Angeles area another marginal heat wave. However, Lane is moving more due west and will be another hurricane to enter waters south of Hawaii midweek. Mega-clusters indicate the favored upper air pattern 1 and 2 weeks from now indicate a transitional pattern from a North-central U.S. trough to ridge (Fig. 2-3). However, the Southwest U.S. and particularly California is not affected by the ridge pattern(s). Regarding ENSO, a Modoki look has definitely developed. The daily Nino4 SSTA regions which is centered on the Dateline in the equatorial West Pacific is a robust +0.95°C and has warmed 0.58°C in the past 30 days. The Nino3 SSTA region in the eastern equatorial Pacific is right at 0.0°C and has cooled slightly the past 30 days. El Nino Modoki remains a possibility for later 2018. Fig. 1: Daily SSTA analysis of the North Pacific basin yields a cooler changes southwest of Baja California. The cooler change defeats support of the upper ridge pattern causing anomalous heat so far in summer 2018 for that region. Another hurricane is headed for the waters south of Hawaii which are El Nino Modoki-like warm. Fig. 2-3: Mega-clusters preferred upper air patterns on August 24 and August 31 clearly identify California as unaffected.