87th AMS Annual Meeting

Wednesday, 17 January 2007: 8:30 AM
Development and Evolution of a Tropical Storm System: Year 2005 Hurricane Katrina Case History
210B (Henry B. Gonzalez Convention Center)
Ayorinde O. Idowu, University of Houston, Houston, TX
It is usually observed that weather in the tropics typically exhibits very little seasonal temperature variation because of year-round high solar altitudes and uniform length. A hurricane is a violent tropical cyclone that originates as a tropical depression, and eventually develops in a mass of warm and humid air. The annual hurricane season, typically from August to November was particularly intensive in the Gulf Coast regions in the Year 2005 with a count of about nine major storms including the Hurricane Katrina that eventually resulted in catastrophic landfalls in Florida and Mississippi areas.

The main objective of this paper is to investigate the origin, tracking, development, and evolution of a severe tropical storm, and thereby evaluate its impact on the physical and socioeconomic environment. A tracking record system reveals the history of Hurricane Katrina from its origin as Tropical Depression 12 (tropical storm),including monitoring of its dynamics as it nears South Florida coastline until the catastrophic landfall as Category 5 Hurricane across the Louisiana-Mississippi border. Katrina then turned westward, and started to intensify as it passed south of Grand Bahamas Island on a heading for south Florida. The Tropical Measuring Mission (TRMM) satellite took its first image on August 25, 2005 while Katrina was passing south of Grand Bahamas Island, and recorded the historical distribution of rain intensity as mostly to the east of the center. Banding features and rainfall were relatively weak at that point in time, indicating that Katrina was still in the process of organizing.

The second image taken displays a 3D perspective of Katrina through the 15dBz isosurface, the vertical height of precipitation-sized particles. The central pressure continued to drop, while the storm began to shift to a more west-northwesterly direction. An image taken on 28 august at 11:24PM just as Katrina was about to become Category 4 hurricane in the central Gulf of Mexico revealed rain intensity from TRMM's sensors as a closed eye surrounded by concentric rings of heavy rain. The intense rain near the core of the storm indicates where heat (latent heat) is being released into the storm that eventually reinforced its kinetic energy, and drives the storm circulation. The height of the eyewall became 16 km, and towers this tall near the core are indicative of intensification as was true with Katrina which later became a Category 4 storm.

The storm intensified into a powerful Category 5 hurricane early on August 28, and Katrina now turned to the northeast in response to a weakness in the subtropical ridge to the north, and an approaching trough from the west. Katrina finally bored down on the north-central Gulf Coast on August 29th, while the large eye of the storm became clearly visible by the Microwave Images (TMI from the TRMM). The first outer bands with embedded areas of heavy rain are already impacting the coast in the southeastern Louisiana. A National Oceanic Atmospheric Administration (NOAA) hurricane hunter aircraft recorded a central pressure of 902mb and sustained winds speed of 175 mph! While the eye eventually crossed the coastline again along the Mississippi-Louisiana border with the most dangerous part of the storm. The resulting catastrophic event caused several huge and massive objects including commercial ships, bridge structures, and offshore drilling rigs to be washed aground. A major portion of the city of New Orleans levee was rifted apart, flooding and submerging most low level land areas in New Orleans.

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