Precedent for North Atlantic TC Season When Main Development Region for Hurricanes is Much Warmer than Normal in June

Fig. 1: In June 2020 the tropical North Atlantic index which represents the sea surface temperature anomaly (SSTA) in the main development region (MDR) for hurricanes in-between the Caribbean Sea and northwest Africa Coast was +0.68 which is a robust warm value. During the past 25 years there are 4 similar analog years. Compared is the remainder of the North Atlantic basin SSTA pattern (using Atlantic multi-decadal oscillation) and ENSO phase (using Nino34 SSTA).

Discussion: The tropical North Atlantic (TNA) index during June 2020 was a robust warm +0.68 ranking 3^rd warmest in the 1995-2020 climate cycle. Other years include 1998, 2005, 2010 and 2017 (Fig. 1). Each year were BIG tropical cyclone seasons with a range of 10-15 hurricanes observed (the 50-year normal is 6.2). The remainder of the North Atlantic basin (using Atlantic multi-decadal oscillation) was marginal to moderately warm each analog year during June. Each analog year was either neutral ENSO or La Nina into the core of the tropical cyclone season. Note that each season had a tendency to produce 3 or 4 primary tropical cyclone tracks (Fig. 2-5).

Summary: In 2020 the likelihood of at least 10 hurricanes given the very warm TNA pattern and no suppressing El Nino is expected! Three of the four analog years produced busy seasons in the Gulf of Mexico and 2020 should be no exception. Given the current Texas/northern Gulf heatwave the Gulf of Mexico is warming fast and now nearly 0.70C above normal, a warm change of nearly +0.40C the past 2 weeks. Expected is a much warmer than normal Gulf of Mexico by August 1^st offering buoyant upper ocean heat for hurricanes later this summer season.

Fig. 2-5: The TNA/MDR analog years and their tropical cyclone tracks, umber of hurricanes and primary tracks for each season.