Fronts and gravity waves in a hurricane: Hurricane Ida (2009)

In November 2009, Hurricane Ida approached the north-central Gulf Coast and made landfall in the Mobile Bay area where the University of South Alabama (USA) Mesonet stations are located. Detailed wind, rainfall, pressure, and temperature data were collected by 14 stations as well as by surface stations from other providers. In addition WSR-88D data are available from the Mobile Regional Airport.

Hurricane Ida (2009) displayed a warm and cold front during its landfall on the north central coast of the Gulf of Mexico. Although the impacts from Ida were minimal, heavy rain exceeding 140 mm over small areas occurred in southwest Alabama ahead of a small warm front. Decreased solar radiation and evaporative cooling form stratiform precipitation ahead of the warm front likely contributed to cooling of the air mass ahead of the front. Onshore flow behind the warm front brought in warm, moist air from the Gulf of Mexico. Detailed surface maps of potential temperature overlain with Doppler radar were used diagnose the evolution of the warm front and the associated rainfall. Timeseries of potential temperature, wind speed and direction, pressure, rainfall, and solar radiation from surface stations provided further details of the front as it passed through. Surface data will be used to estimate terms in the frontogensis equation.

Regular oscillations were detected in the 1-min surface pressure timeseries of USA Mesonet stations ahead of the surface front. Further investigation indicates these might be gravity waves. Power spectra and other analyses will be presented to confirm this.