WMO forecasts record Pacific warmth of 3.7C above normal as El Niño builds toward a December peak

WMO's record claim compares a forecast with an observation. The October-to-December anomaly is a predicted seasonal average. The November 2015-to-January 2016 mark it would replace was measured ^[4]. The two windows overlap by two months, and the forecast clears the old record by 1.1C ^[18]. An El Niño is declared once those waters run 0.5C above normal ^[17].

The observed climb points the same way. The Niño 3.4 index gained 0.9C between June and August ^[19]. Reaching the forecast seasonal mean would take roughly another 1.2C beyond the August reading ^[20].

The update expects the event to keep strengthening until its December peak ^[1]. According to WMO, the persistence probability is a consensus of 13 national and international centres working from shared ocean buoy, satellite and radiosonde data ^[11]. "El Niño is firmly established and strengthening rapidly. WMO forecasts indicate a nearly 100% likelihood that it will persist through February 2027, potentially being one of the strongest since at least 1950," WMO Secretary-General Celeste Saulo said ^[2]. Her wording is more careful than the index forecast. The sea surface anomaly is forecast to set a record, while the event as a whole is described as potentially one of the strongest since at least 1950.

Saulo gave the physical reason at the Global Heat Forum in Bangkok. "El Niño doesn't add new heat to the planet. It releases heat the ocean has already been storing beneath the surface," she said ^[5]. "The ocean it's drawing from is the warmest we've ever measured it. There is simply more heat available to release," she said ^[6]. Global sea surface temperature reached an all-time observed high in August ^[12].

The thing this update doesn't tell you is what any single site will see. Its rainfall signals mark where wetter or drier seasons are more likely, and WMO says they are not a substitute for national and local forecasts ^[13]. The temperature call is an overwhelming likelihood of above-average conditions across large areas, measured against a 1993-2009 baseline. That does not mean every place is warmer every day ^[7]. Wetter seasons are favoured in the Greater Horn of Africa, parts of Central Asia and coastal East Asia, the northern Arabian Peninsula, parts of North America south of 45 degrees north, and southeastern South America ^[14]. Drier ones are forecast for the Indian subcontinent and the western Pacific, with a dry band running across the South Pacific to the southern tip of South America ^[15]. A positive Indian Ocean Dipole, a pattern that can strongly influence rainfall around that ocean, is expected to peak in October and then decline ^[16].

In India, the dry outlook follows a monsoon that the Indian Express says El Niño weakened in its second half ^[8]. Maharashtra and Karnataka are among the states that have declared drought, and Maharashtra has imposed a 10% water cut in many of its districts ^[9].

I think the persistence forecast is firm enough to treat as a fixed condition through February. The regional maps are less firm. They shift odds over large areas, and a plan for one site needs the national service's outlook as well ^[13]. The only mortality estimate in these reports comes from the University of Chicago's Climate Impact Lab. Last month it projected as many as 451,000 excess deaths worldwide from June to February 2027, the Independent reported ^[21].