From late Sept. through early Oct. 2021, two powerful storms churned over the Pacific and Atlantic Oceans: Typhoon Mindulle, which peaked as a Category 5 storm, and Hurricane Sam, a Category 4 hurricane and one of the longest-lived hurricane-strength storms on record over the Atlantic Ocean. While neither storm posed a direct threat to land, Mindulle brushed by eastern Japan, leaving heavy rainfall accumulations in the area near Tokyo. Despite the fact that neither storm made landfall, the storms’ slow-motion tracks across warm ocean waters allows an opportunity to observe how the strong winds and deep clouds that accompany tropical cyclones affect the underlying ocean surface.

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The above animation shows the rain rates (blue/yellow shading) and accumulations (green/purple shading) produced by the two storms from Sept. 22 through Oct. 2, 2021, estimated by NASA’s IMERG algorithm. IMERG is a multi-satellite precipitation data product that provides global, half-hourly estimates of rainfall over land as well as the ocean. Cloudiness is shown in shades of white/gray below the rain rates, based on geosynchronous satellite infrared observations. Once the storms complete their track northward, the animation transitions to a series of snapshots of sea surface temperature (SST) based on NASA’s MUR multi-satellite SST product. Red and blue shades show warm and cool differences, respectively, between each day of the animation and September 22, when each storm was just beginning to form.

Typhoon Mindulle was remarkable in contrast to Hurricane Sam most notably for its large size, which is apparent throughout the animation and also in the final rain accumulation estimates. Mindulle was estimated to have produced accumulations during this 11-day time period well in excess of 18 inches over a large area (dark purple shading), while Hurricane Sam only produced isolated patches of precipitation at those levels. In addition to producing heavy rainfall, tropical cyclones cool the ocean surface as they pass over it, largely due to strong winds stirring up cool waters from below. The ocean surface cooling is also a result of the cyclone extracting heat and moisture from the ocean, and in the process, sustaining the motion and rainfall within the storm itself. Mindulle’s large radius and strong winds contributed to the strong cooling of the ocean surface along its track, which exceeded 3 degrees Celsius (dark blue shading) over much of the northern portion of its track. Sam, by contrast, only cooled the ocean by approximately 1 degree Celsius along much of its track. The reasons for the differences in cooling between storms are often related to variations in the subsurface properties of the ocean, and are an active area of research for many strong tropical cyclones.

NASA’s fleet of Earth-observing satellites allows scientists to study the interconnections between components of the Earth system, such as the atmosphere and ocean, contributing to an improved understanding of the processes that lead to extreme events. 

Credits:

Story and Animation by Jason West (NASA GSFC / PPS)