Observed Ocean Heat Content Variations From In-Situ and Satellite Measurements During The 2017 Hurricane Season

A 20-year time series of satellite-derived oceanic heat content (OHC) estimates relative to 26^oC has been generated from quality controlled sea surface height anomaly (SSHA) fields from various missions (e.g., Jason 1-3, Envisat, SARAL, Cryosat-2, Sentinel-3A) cast into a 2.5 layer reduced-gravity ocean model and a daily ocean climatology of mean isotherm depths and reduced gravities. Over this time/space series, two or more satellites have been operational at any given time to resolve mesoscale ocean variability. Sea surface temperatures (SST) from the NESDIS SST Analysis represent the surface boundary condition to produce isotherm depths of the 20^o and 26^o (D20, D26), mixed layer depth, and OHC. For the operational product suite, SSHA data from 10 days before the date in question are used. By contrast, the reprocessed data uses SSHA data from 5 days before and 5 days after the date of interest for more detailed research product including those with longer repeat tracks so mesoscale oceanic features were not unnaturally stretched out. The resulting data products date back to 1998 for three basins. As part of the product generation and updating the climatologies, satellite-derived estimates have been compared to over a million in-situ thermal measurements from multiple platforms (e.g., Argo and APEX Floats, ship transects, moorings, expendables) to assess biases and uncertainties in space-based estimates and to adjust climatologies.

Implications of OHC variations on hurricane intensity will be discussed for Harvey and Nate (2017) over the Gulf of Mexico and Irma and Maria (2017) over the western Atlantic Ocean basin. Harvey, Irma and Maria (2017) rapidly intensified over deep warm thermal layers (OHC > 80 kJ cm^-2) to severe status under favorable atmospheric conditions. Harvey intensified over a warm eddy that was separated from the Loop Current several months earlier in the eastern Gulf of Mexico. During Irma, several eyewall replacement cycles were observed as the storm moved over high OHC water resulting in an expanded wind field encompassing the entire peninsula of Florida during landfall. Maria rapidly intensified over high OHC water in the eastern Caribbean Sea. Finally, hurricane Nate developed in the western Caribbean and moved northward over the Loop Current that included an array of APEX-EM floats at a category 1 status. To complement these in-situ measurements, pre, during and post-storm ocean profiles were acquired by deploying expendable ocean profilers from the NOAA WP-3D to assess the OHC levels in the eastern Gulf and their relationship to the air-sea fluxes and the moisture disequilibrium.