We know that the Caribbean Sea, the Gulf of Mexico and the Western Tropical North Atlantic are very important regions for the genesis and strengthening of tropical cyclones. In August 2019, Hurricane Dorian devastated part of the Bahamas when it underwent rapid intensification and transitioned from category 4 to category 5 hurricane. None of the operational hurricane forecasting models were able to predict this rapid intensification event and consistently all of the models under predicted the intensity evolution of Dorian. In the last three decades there has been a good progress reducing the error in the storm track but the error reduction in the intensity has been marginal. One of the reasons for this is the difficulty modeling the upper ocean processes that affect the air/sea heat fluxes under tropical cyclones. 

Our main objective in this work is to evaluate several upper ocean metrics that are relevant to air/sea heat fluxes and therefore to hurricane intensity in the HWRF-POM operational and experimental model and the HWRF-HYCOM experimental model during Hurricane Dorian. For this, we used temperature and salinity data from a fleet of underwater gliders that were deployed in the Caribbean during the 2019 hurricane season.  

One of the tools that we used to visualize the model’s performance is the Taylor diagram. A Taylor diagram is polar plot in which the radial axis is the standard deviation and the angle is the correlation between the model and the observations. The closer the model estimate in this diagram is to the observations, located on the 1 on the standard deviation axis, the better the model skill. 

One of our main results is that even though all models have a good skill in the temperature and salinity of the entire water column, the model’s skill considerably deteriorates for the upper ocean metrics that we evaluated, such as temperature in the mixed layer, ocean heat content and depth average temperature in the top 100 meters. This demonstrates that the ocean models underneath the hurricane forecasting models still need improvement in the fields that are relevant to the air/sea heat fluxes.

Finally, we started to investigate the influence of the barrier layer in the Caribbean Sea on vertical mixing processes, which also affect the air/sea heat fluxes. We found that there is clear evidence that during the passage of Dorian vertical mixing was inhibited by the presence of the barrier layer. However, none of the models captured the strength of the barrier layer and its effect on vertical mixing. 

Please come a visit my poster and thanks for listening!