Graduation Year

2011

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geography, Environment and Planning

Major Professor

Jennifer M. Collins

Keywords

ArcGIS, Gr2Analyst, hazards, precipitation, spatial analysis

Abstract

Pinellas County is located on a peninsula in Florida that experiences daily patterns of sea breeze associated rainfall mainly during the summer months of June through August. Previously, rainfall patterns, amounts and timing and severe weather in Pinellas County have not been examined considering dominant wind flow patterns, sea breeze circulations and other atmospheric variables. To improve forecasting of local mesoscale phenomena, this project examined the rainfall patterns, amounts and timing and severe weather occurrences that occur as a result of sea breezes and associated prevailing wind regimes within Pinellas County for the months of June, July and August for the years 1995-2009. Other atmospheric variables are also considered.

Through the use of sounding data from the Ruskin, FL National Weather Service (NWS) Station, Pinellas County rainfall station data, and radar-estimated rainfall totals data from the NWS Advanced Hydrologic Prediction Service, the following meteorological parameters were examined: dominant wind direction and speed, stability (convective available potential energy, CAPE and CAPEV; CAPEV is CAPE calculated using virtual temperature). Composites were made of radar-derived rainfall estimates to show where the dominant rainfall occurs in relation to the sounding classifications of dominant wind flow for that day using ArcGIS as an analysis tool. Composite maps of precipitation indicate that the largest range of precipitation across Pinellas County occurs when winds are from the 241-300° direction category. The soundings were also used to classify days by CAPE, wind speed, and precipitable water. Precipitable water had a significant positive correlation with precipitation amounts in four of the five wind direction categories. Wind speed had significant positive relationships with a southerly wind direction. In order to examine the timing of rainfall associated with each wind direction category, Gr2Analyst was used. Gr2Analyst indicated rainfall occurred earlier in days featuring a westerly flow, and later in days with an easterly flow.

Severe weather is also influenced by wind regimes and other atmospheric variables. Wind direction, wind speed, CAPE, precipitable water, and the United States Air Force Severe Weather Threat Index (SWEAT) indices were examined in relation to severe weather. The likelihood of severe weather was related to wind direction, with more events occurring during days with a more easterly flow than westerly. Atmospheric parameters were also examined in relation to each severe weather event.

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