El Nino, Marine Heat Waves, and July 2023 Northern Hemisphere Climate Risks

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Executive summary: Evolving El Nino coupled with marine heat waves suggest the warmest global ocean temperatures on record are ahead for 2023. As of March, global SSTA were the 3rd warmest in 174 years. Certainly, the super warm global SSTA will influence climate patterns. Of leading interest is where drought areas emerge during the northern hemisphere summer. Right now, concern areas are tropical SSTA-driven drought in Western Indonesia and possibly India while MHW-driven drought returns to Europe and the U.S.

Fig. 1: Current global SSTA analysis from the University of Maine Climate Re-analyzer with ENSO/MHW annotations.

Discussion: March 2023 was the 3rd warmest global sea surface temperature anomaly (SSTA) regime in the 174-year climatology. The previous record warm March was in 2016 when one of the strongest El Nino episodes on record reached mature stage coupled with the surprisingly intense gigantic marine heat wave (MHW) covering the Northeast Pacific basin. Right now, El Nino is re-developing, and the Northeast Pacific basin (MHW) is still out there although displaced westward to the north of Hawaii.

Contributing to the recent persistence of record or near record warm global SSTA is the increasing presence and intensity of MHW episodes. MHW’s are areas of very warm SSTA at the surface and at depth up to 300-400 meters that extend across many 100’s of miles and last several months to several years. The specific cause of MHW’s is not well understood.

Most ominous now is the ferocious warming of the ocean surface off the Northwest Africa Coast and the Western Mediterranean Sea. A common climate correlation in the atmosphere to these massive MHW episodes is anomalous high-pressure which increases drought and hot weather risk during the summer season. The MHW in the Mediterranean Sea in 2022 was the catalyst to the drought and attendant heat that left the Rhine River nearly dry. Is this regime redeveloping?

MHW’s have become semi-permanent surrounding New Zealand and east of Argentina. Another new MHW has emerged in the Southwest Indian Ocean. A peculiar area of very warm sea surface temperature anomalies (SSTA) exists over the tropical West Pacific/Maritime Continent area. Normally, if El Nino is ahead, this area turns cooler as trade winds increase. As Q2/2023 arrives, both the far eastern equatorial Pacific and the tropical West Pacific contain exceptionally warm SSTA forecast to merge and create a Pacific tropics-wide warm anomaly just after mid-year (Fig. 2) certain to trigger the warmest ocean surface year on record possibly coupled with equally warm land mass temperatures for 2023.

The super warm SSTA pattern forecast to strengthen through northern hemisphere summer causes temperature anomaly forecasts to indicate anomalous hot summer temperature risk in the U.S. and Canada, Europe, Central Russia plus the Korean Peninsula and Japan (Fig. 3). ENSO-driven forecasts indicate dry/drought areas are likely in Western Indonesia and possibly India (Fig. 4). MWH-driven patterns could trigger drought in Europe and the U.S.

Fig. 2: NCEP CFS V2 global SSTA forecast for July 2023 with various annotations of warm SSTA zones.

Fig. 3: NCEP CFS V2 global temperature anomaly forecast for July 2023 with hot weather risk for northern hemisphere mid-summer highlighted.

Fig. 4: NCEP CFS V2 global precipitation anomaly forecast for July 2023 with dry weather risk for northern hemisphere mid-summer highlighted.