The mathematical models used to make predictions on the nowcast are based on measurements of environmental and water-quality variables known to influence E. coli levels. These are called "explanatory variables" and include measurements of rainfall, wave height, and water clarity.
During 2009, two models will be used at Huntington and three models will be used at Edgewater. Which model is used is based on the date; that is, a different model is used at the beginning of the season than at the end of the season. Using different mathematical formulas and different variables in the models for different times of the year will hopefully minimize the percentage of incorrect predictions provided by the models in 2009.
At Huntington, the variables used in the models for the 2009 nowcast are as follows:
Subseason 1 (May 18−July 23): (1) log turbidity (the logarithm of the measured water clarity), (2) radar rainfall from six 4-km grids surrounding the beach during the previous 24 hours, and (3) day of the year. The threshold probability for issuing an advisory using this model is 23 percent.
Subseason 2 (July 24−Sept 7): (1) Wave height and (2) radar rainfall from six 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight. The threshold probability for issuing an advisory using this model is 26 percent.
Subseason 1 (May 13−June 8): (1) Wave height and (2) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight. The threshold probability for issuing an advisory using this model is 22 percent.
Subseason 2 (June 9−Aug 10): (1) Wave height, (2) log turbidity (the logarithm of the measured water clarity), (3) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight, and (4) day of the year. The threshold probability for issuing an advisory using this model is 27 percent.
Subseason 3 (Aug 11−Sept 15): (1) Wave height, (2) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight, and (3) day of the year. The threshold probability for issuing an advisory using this model is 32 percent.
