The North Atlantic warm hole (NAWH) is exceptionally strong during summer 2025 well-correlated to a semi-permanent upper-level trough across the same area recently budging eastward toward Europe the first half of September. Proximity of the trough to Europe has spawned heavy rains for late calendar-summer. The ECM ENS 10-day rainfall forecast indicates the emphasis of the heavy rain consolidates over France and vicinity.

In North America, the late summer 2025 weather pattern forecasts were most effective during the 6-10-day utilizing ECM ENS, traditionally the best operational model. In second place, AIFS ENS continued to score well since the July 1st debut. ECM ENS and AIFS ENS have routinely scored no. 1 and 2 for medium-range forecasts during mid-to-late calendar summer 2025.

Emergence of the marine heatwave in the Northeast Pacific potentially increases the risk of El Nino in 2026 as the anomalous warm water spreads to the tropics. The NCEP CFS V2 Nino34 SSTA forecast continues to edge into El Nino territory Q2/2026. The change in ENSO will be applied to new season 1-4 ahead forecasts. The upcoming La Nina is a relatively short duration episode.

Merging between marine heatwave (MHW) NEP25A and NEP25B occurred during late AUG/early SEP as exceptionally warm sea surface temperature anomalies (SSTA) reached the West Coast of North America in the Northeast Pacific. The warming water surface episode is similar with the previously strongest warming event observed during 2013-16, commonly referred to as the “warm blob”.