Long Term Trends in National Hurricane Center Watches and Warnings
Mark DeMaria Mark.DeMaria@noaa.gov NOAA/NESDIS/ORA/RAMMB Fort Collins, CO
James L. Franklin James.Franklin@noaa.gov NOAA/NCEP/TPC Miami, FL
The National Hurricane Center (NHC) is responsible for issuing hurricane watches when hurricane force winds (64 kt or greater) are possible within the next 36 hours and hurricane warnings when hurricane winds are expected within the next 24 hours. The watches and warnings (WWs) for the contiguous U.S. are examined for the period 1963- 2006. The coastline lengths included in the WWs are calculated and the regions along the coast that experienced hurricane winds are estimated using the NHC radii of hurricane forecast winds and best track storm positions. The time of first arrival of hurricane winds is also estimated using the radii and best track so that the lead times from when the WWs were first issued for a given location can be calculated. Results show that the size of the average warning areas steadily increased by decade from the 1960s to the 1990s, despite the considerable improvement in track forecasting. During this period the track forecast improvement was being utilized to improve the lead time of the warnings, which increased from 22 h in the 1960s to 30 h in the 1990s. In the 2000s the trend of increasing warning lengths was reversed and the lead time was further increased. The average length of the hurricane watches by decade steadily decreased and the average lead times steadily increased from the 1960s to the 2000s. Results also show that in the 2000s the average lead time of the warnings is considerable longer than 24 h, and the average lead time of the watches is longer than 36 h.
The views, opinions, and findings in this report are those of the authors and should not be construed as an official NOAA and/or U.S. Government position, policy, or decision.