Two maps are available at each analysis or forecast time: A map showing the minimum attainable central pressure of tropical cyclones (mb), and a map showing the maximum sustainable surface wind speed. The latter is the maximum gradient wind at low levels reduced by 20% to account for the reduction of surface winds by friction. The method used in calculating these quantities is described in a separate document, Limits on Hurricane Intensity. Experience using potential intensity estimates based on climatology indicate that few, if any, storms will ever exceed the potential intensity value; most storms will not achieve their potential intensity:
Actual Versus Potential Intensities
[Fig.1: Observed minimum central pressures (abscissa) versus potential minimum pressure (ordinate) calculated using climatological SST's and atmospheric profiles at the locations of observed Atlantic hurricanes. Courtesy of Dr. Lars Schade.]
On the other hand, there has been almost no experience to date using potential intensity calculations from real-time data. Hurricanes cannot be expected to develop where the potential intensity estimate is small or zero; but storms moving rapidly from regions of high potential intensity to regions of low intensity can be expected to maintain strength well in excess of the local potential intensity estimate.
Where a storm already exists and its presence is reflected in the NCEP data, the potential intensity estimate may be in error at the location of the storm, because the calculation of the potential intensity assumes that the vertical sounding is an environmental sounding.
Atmospheric data used in these calculations reflects the latest data set available from NCEP; generally the 1 X 1 degree gridded data. Sea surface temperatures are updated weekly. The date on the maps is that of the atmospheric gridded data used.
Location of maps
Obtain the Maximum Potential Hurricane Intensity Maps here. I am most grateful to Jim Kinter, Paul Dirmeyer, Brian Doty and Jennifer Adams of the Center for Ocean-Land-Atmosphere Studies for preparing and maintaining these maps. Information about the graphics package used to make these charts as well as other weather information can be obtained directly from the COLA Home Page.
Please direct any comments about the format of the maps or the algorithm used to calculate potential intensity to me at (mylastname) at mit.edu
Kerry Emanuel 1 July 1996