HWRF HDFL/HD12 Forecast Comparison

HDFL/HD12 Forecast Comparison Executive Summary

    • The DTC conducted an extensive testing and evaluation activity to compare the error characteristics of two sets of runs: a control configuration very similar to the HWRF 2012 operational configuration (HD12), and a variant in which the fluxes of momentum, sensible, and latent heat in the ocean were altered (HDFL).

    • The alteration in ocean fluxes, making their value more physically-based, was prompted by an evaluation of the ocean response performed by AOML/HRD. Their analysis showed that post-storm cooling in HWRF was weaker than observed.

    • For each of the two HWRF configurations, 750 HWRF retrospective forecasts for the 2012 seasons of the Eastern North Pacific and Atlantic basins were conducted in order to produce a large sample from which robust conclusions could be derived.

    • The main difference between the HDFL and HD12 results is the intensity bias for the Atlantic. The positive bias seen in HD12, which grows throughout the forecast, is not present in HDFL, which has near-zero bias.

    • In the Pacific, both HD12 and HDFL have negative biases and they are very similar. It is possible that the one-dimensional POM-TC configuration in the Pacific (as opposed to the three-dimensional configuration used in the Atlantic) lessens the impact of the flux changes in the Pacific.

    • Virtually no statistically significant differences in track errors were noted between the two configurations.

    • Small, but statistically significant, differences in storm structure error were documented for a few quadrants, wind threshold, and forecast lead times. In the Pacific most favored the HD12 configuration, while in the Atlantic most favored the HDFL configuration.

    • The superiority in intensity bias in the Atlantic basin for the HDFL configuration can be attributed in large part to forecast improvements for Leslie (12L). Leslie was a large slow-moving storm, possessing characteristics that maximize the ocean-atmosphere interaction.

    • Model output files have been archived and are available to the community for future studies. Forecast maps and verification graphics, along with this report and additional information are available in the DTC website.

    • The results obtained for the HD12 configuration will be used to designate DTC Reference Configuration HWRF PS:85.98.98.88.88.2.84.