Oceanic Influences on Super Typhoon Haiyan

From 3 to 12 November 2013, typhoon Haiyan rapidly intensified to a super typhoon (ST) status along the northern perimeter of the western Pacific warm pool. During its passage, several ARGO floats provided pre and post temperature measurements to as deep as 1000 m close to the best track. In addition, Haiyan made a direct hit on a NOAA TAO buoy located at 8°N, 137°E where temperature, salinity and current measurements were also acquired as the typhoon was going to ST status. These data along with satellite fields derived from the Systematically merged Pacific Ocean Temperature and Salinity (SPORTS) climatology are used to examine the levels of presumed warming in the thermocline prior to the Haiyan as well as documenting the levels of the oceanic response. Note the SPORTS derived product using satellite fields has been carefully evaluated with more than 267,000 thermal profiles over a 12-year period.

Initial reports suggested that the level of warming at 100 m depth exceeded 5°C. Subsequently the levels of warming were decreased to 3°C by comparing float profiles to a climatology. However, closer examination of the available data, albeit sparse suggests considerably lower levels of pre-Haiyan warming in the thermocline. That is, this area of the western Pacific ocean basin has long been recognized as an area of vigorous internal tides at the semidiurnal frequency. The thermal excursions of the temperature profiles can be seen as ± 2.5°C. Indeed when comparing ARGO float data profiles to climatologies, the temperature profiles suggests as much as 3°C compared to a climatological temperature at 100 m. However, the floats do not account for these large excursions induced by the internal tide. By using available mooring records, the differences between climatologies are less than 1°C and in some cases 0.5°C. Moreover at the mooring, there is little evidence of substantial ocean cooling (typically less than 1.5°C), evidence of roughly 20 to 30 m deepening of the surface mixed layer, and roughly 10 to 20 m upwelling induced by the wind-driven currents associated with Haiyan. There was little evidence of a barrier layer (e.g. halocline) in the surface mixed layer that may have affected mixing. In short there was minimal ocean response associated with this ST, thus there was clearly more OHC (~120 to 140 kJ cm^-2) and warm SSTs (>28°C) providing heat and moisture to the ST. These intensity fluctuations are in fact similar to those observed in the northwest Caribbean Sea. That is, minimal ocean cooling response and more sustained fluxes to the atmosphere regardless of the translation speed lead to stronger storms especially when atmospheric conditions are favorable.