21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction

6B.5

Examining planetary, synoptic, and mesoscale features that enhance precipitation associated with Tropical Cyclones making landfall over North Carolina (Formerly Poster P1.62)

Meredith S. Croke, UCAR/COMET, Raleigh, NC; and M. L. Kaplan, L. Xie, and K. Keeter

Many factors influence the intensity of precipitation proceeding, during and after landfall of tropical cyclones. A three-part study of all tropical cyclones that have made direct landfall on the North Carolina coast, will aid in determining the most important planetary and synoptic scale circulation features involved in forecasting precipitation intensity. This research will incorporate a precipitation analysis, a planetary/synoptic scale analysis as well as model runs to examine the meso- and meso- scale features that are necessary for enhancement of precipitation during landfall.

Fifty-two stations across six climate regions of North Carolina were used for the Quantitative Precipitation Forecast (QPF) portion of this study. The six climate regions include the Northern Piedmont, Central Piedmont, Southern Piedmont, Northern Coastal Plain, Central Coastal Plain, and Southern Coastal Plain. Daily rain gauge data of twenty-eight storms dating back to 1953 was used for the precipitation analysis. Since there are no specifications on when rain gauge data should be collected, some of the data may have been collected in the early hours of the day, while other data may be collected in the evening. To account for this potential discrepancy, three-day rainfall totals were used in this study. These totals accounted for precipitation that occurred prior to, during, and after landfall.

The three-day precipitation totals from 52 stations across the six climate regions were arithmetically averaged, for all twenty-eight tropical cyclones. This number became the benchmark to classify storms as heavy or light rainfall events. If a storm received greater precipitation then the average number it was considered a heavy rainfall event. There were 14 storms in each the heavy and light rainfall categories. ARCGIS was used to create krigged analysis of precipitation.

National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) 2.5 x 2.5 degree grid scale reanalysis data was used for all maps and statistics. Higher resolution 36 km North American Regional Reanalysis (NARR) data was also used for the climatology portion of this study. Composite analyses of features such as 250 mb geopotential height, precipitable water and lower and upper level potential vorticity were produced to examine the signals in each of the groups, with statistics verifying all data.

The 90-level Stratospheric Non-Hydrostatic Mesoscale Atmospheric Simulation System (NHMASS) numerical model will be run to complete the synoptic, Meso-α and Meso-β scale analyses of this study. The model will be run on a heavy and light rainfall event, Hurricane Floyd and Tropical Storm Arthur, respectively. The synoptic scale analysis will be performed using a 36 km grid scale run 72 hours prior to landfall, while the Meso-α scale will focus on central and eastern United States with an 18 km grid beginning 36 hours prior to landfall. The Meso-β scale will center on the mid-Atlantic coast and Appalachians with a grid scale of 6 km and begin about 12 hours prior to landfall. Examining features at this small scale will allow us to study jet features, the presence of a coastal front and inverted troughs. All of these features are extremely important to predicting the intensity of precipitation associated with a tropical storm from 12 hours prior to landfall, until shortly after landfall. Running the NHMASS model will allow for the creation of a paradigm describing heavy rainfall events up to 72 hours prior to landfall, utilizing data from all four time scales.

extended abstract  Extended Abstract (852K)

wrf recording  Recorded presentation

Session 6B, Tropical Forecasting
Tuesday, 2 August 2005, 8:00 AM-9:15 AM, Empire Ballroom

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