Controlling Mechanisms on Tropical Storm Hermine (2022) and Their Sensitivity to CPEX-CV Observations

Tropical Storm Hermine was an unusual storm developing east of Cabo Verde with a northward track. Hermine began as a tropical wave over West Africa and propagated over the Atlantic while interacting with a dust rich Saharan Air Layer (SAL) to its west. Two CPEX-CV flights sampled Hermine and the SAL in the data sparse region during the early stages of Hermine. In this study we used the Weather Research and Forecasting Dust model and the Gridpoint Statistical Interpolation analysis system to assess the impacts of assimilating CPEX-CV observations on the forecast of Hermine and the impacts of the SAL on Hermine’s development. Temperature, moisture, and wind observations from the suite of remote sensing and in situ instruments are assimilated leading to an improved track and intensity forecast. Assimilating CPEX-CV observations weakened the strength of mid-level easterlies aiding in the forecast of the unusual northward movement. A more developed circulation was also present in the initial analysis providing upper-level vorticity for Hermine’s genesis. The intensity of Hermine is stronger and was able to capture the strengthening of Hermine into a tropical storm while without assimilating CPEX-CV observations barely produced tropical depression strength winds. A sensitivity test is also conducted to determine whether cooler sea surface temperatures lead to the weakening of Hermine.