A significant predictor for numbers of the most intense storms is the presence of warmer-than-normal deep tropics ocean water as measured by the tropical North Atlantic (TNA) index. During the past 25 years the North Atlantic tropics have typically been somewhat warmer than normal during the core of the tropical cyclone season.

The preliminary outlook indicates MAY-SEP 2021 is hotter than last year as the average of the U.S. cities CDD forecast is about 112% of the 30-year normal compared to just-under 109% last year. Meteorological summer (JUN/JUL/AUG) is not quite as hot as last year.

Last week southern oscillation index returned to weak positive phase and trade winds off the northwest coast of South America also returned. As a result, the increased trade winds up-welled cool waters to cause all Nino SSTA regions to fall to within La Nina thresholds. However, the subsurface at 75+ meters continue to warm and subsurface cool water supply to sustain La Nina is steadily losing amplitude.

A titanic blocking high-pressure ridge south-southeast of Australia during the past 5+ days forced a deep upper trough to form along the southern Australia Coast this past weekend and into this week. Tropical moisture entrained into the upper trough from a warmer-than-normal water surface north and northeast of the continent lead to the 60-year flooding episode in Sydney and surrounding areas.