Currently, Climate Impact Company is monitoring 8 marine heat waves (MHW). Most prominent is MHW NEP23A in the Northeast Pacific. The core of MHW NEP23A has strengthened to the north of Hawaii. However, the eastward extension to the West Coast of North America earlier during summer 2023 is now weakening.

The latest seasonal totals so far assembled by Colorado State University (CSU) indicates 11 tropical storms have formed with 3 reaching hurricane strength including 2 major hurricanes. The accumulated cyclone energy (ACE) index is 48.6 compared to the normal value for this date of 36.3. Using the ACE index, the 2023 season so far is judged about 33% more intense than normal.

Let’s take a quick look at verification of Climate Impact Company constructed analog forecasts, made in late April, for June and July 2023. A constructed analog forecast is based on regional SSTA patterns and their historical relationship to upper air patterns that drive our sensible weather.

In the North Pacific, an immense MHW has strengthened across the northwest basin. Similarly, MHW NEP23A in the northeast Pacific has strengthened and shifted to the northwest coast of North America. In the North Atlantic basin, the North Atlantic warm hole (NAWH) recently shifted to coastal West Europe. However, the rapid development of a MHW off Newfoundland during late spring is now weakening quickly. The MHW off northwest Africa extending to the western Mediterranean Sea has weakened slightly.