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Annual Tropical Cyclone Report 2020

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Executive Summary

This Annual Tropical Cyclone Report (ATCR) was prepared by the staff of the Joint Typhoon Warning Center (JTWC), a jointly manned United States Navy / Air Force organization.

The Joint Typhoon Warning Center was officially established on 1 May 1959 when the Joint Chiefs of Staff directed the Commander-in-Chief, US Pacific Command (USCINCPAC), to provide a single tropical cyclone warning center for the western North Pacific region. USCINCPAC delegated the tropical cyclone forecast and warning mission to Commander, Pacific Fleet (PACFLT), and subsequently tasked Commander, Pacific Air Force (PACAF) to provide tropical cyclone (TC) reconnaissance support. Since 1959, JTWC’s area of responsibility (AOR) for its TC forecast and warning mission has expanded to include the area from the east coast of Africa to the International Dateline in the northern hemisphere, and from the east coast of Africa to the west coast of the Americas in the southern hemisphere. JTWC also monitors TC activity in the eastern and central Pacific Ocean, coordinating with the National Hurricane Center and Central Pacific Hurricane Center to promulgate warnings and provide tailored support to DOD customers. Altogether, this AOR encompasses over 63-million square miles of tropical oceans, and includes portions of five geographic combatant commands. Accurate and timely TC warning and decision support products from JTWC protect life and property of U.S. assets, and enable DOD commanders to sustain operations across an area within which over 80% of global tropical cyclone activity occurs annually.

This edition of the ATCR documents the 2020 TC season, and describes operationally or meteorologically significant cyclones that occurred within the JTWC AOR. Details highlight significant challenges and/or shortfalls in the TC warning system and serve as a focal point for future research and development efforts. Also included are TC reconnaissance statistics and a summary of TC research and development efforts, operational tactics, techniques and procedure (TTP) development, and outreach that members of the JTWC conducted or contributed to throughout the year.

Across all forecast basins for the 2020 storm season (1 January 2020 through 31 December 2020 for the Northern Hemisphere and 1 July 2019 through 30 June 2020 for the Southern Hemisphere), JTWC produced 757 warnings1 for 58 TCs, or 789 warnings for 61 TCs during the 2020 calendar year (not shown). Additionally, JTWC repackaged 316 warnings for cyclones in the eastern and central Pacific basins. Figure P-1 (below) shows the timeline of JTWC-warned tropical cyclone activity across the JTWC AOR for calendar year 2020. In Nov, 2017, JTWC began issuing warnings at 6-hour intervals for all southern hemisphere TCs. Beginning with the 2020 southern hemisphere TC season, JTWC once again modified its policy in order to balance workload. Figure P-2 depicts the areas of 6 and 12 hour forecast frequency for the southern hemisphere.

In the western North Pacific (WESTPAC), the year began with ENSO neutral conditions and transitioned to a weak La Niña event beginning in August, based on the Oceanic Niño Index for the Niño 3.4 region. JTWC’s total of 26 numbered tropical cyclones was below the long-term mean of 30, while the accumulated cyclone energy (ACE) of 155.7 units was well below the 20-year mean value of 274.2.

WESTPAC mean absolute errors (MAE) for track forecast improved, breaking or tying records across all lead times. The five-day 155.7 nm MAE, in particular, was only 6 nm above the 2009 US INDOPACOM forecast goal. On the other hand, four and five-day intensity forecast skill compared to climatology and persistence fell sharply. However, skill at 1-2 day lead times improved to new highs, in part due to recent improvements in rapid intensity change detection and prediction.