Ocean Model Impact Study for Coupled Hurricane Forecasting: An HFIP Initiative

In December 2014, the NOAA Hurricane Forecast Improvement Project (HFIP) formed the Ocean Model Impact Tiger Team (OMITT) consisting of model developers and research scientists as one of HFIP working groups. The primary objective is to evaluate the impact of ocean coupling in tropical cyclone (TC) forecasts. Category 3 Hurricane Edouard in 2014 is an excellent real case for the ocean model impact study, given the availability of ocean observations before, during, and after storm passage. Three Eastern North Pacific (EPac) Hurricanes for 2015, Blanca, Dolores and Patricia, are also of special interest because the ocean appeared to have a significant impact on intensity evolution. The first two powerful Category 4 storms followed a similar track, but forced dramatically different ocean cooling, ~7.2oC and 2.7oC in response to forecast intensity of 40 ms-1 and 20 ms-1, respectively. Hurricane Patricia was the strongest hurricane ever recorded in EPac, having sustained winds of 175 kt following rapid intensification (120 kt over 30 hours). Operational guidance models were all unable to predict the maximum wind and rapid intensification. The EPac 2015 season was affected by El Nino which produces anomalously warm conditions. Preliminary results suggest that the ocean model initialization must not only reproduce the anomalous seasonal heat content, but also reproduce the energetic mesoscale eddy features in the region. Two versions of operational HWRF along with the COAMPS-TC prediction system are employed in the study. Impacts of ocean coupling and ocean model complexity are assessed by comparing uncoupled forecasts to forecasts with both 3D and 1D ocean model coupling. Future plans are discussed with respect to the use of ocean OSSEs to evaluate observational strategies to improve model initialization, and also with respect to evaluating the performance coupled prediction systems in terms of their capability to accurately reproduce important physical processes governing ocean-wave-atmosphere coupling.