Editorial Type:
Article
Article Type:
Research Article

Numerical Investigations on the Formation of Tropical Storm Debby during NAMMA-06

Sen Chiao Department of Maine and Environmental Systems, Florida Institute of Technology, Melbourne, Florida

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Gregory S. Jenkins Department of Physics and Astronomy, Howard University, Washington, D.C

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Print Publication:
01 Jun 2010
Collections:
West African Weather Prediction and Predictability
DOI:
https://doi.org/10.1175/2010WAF2222313.1
Page(s):
866–884
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Abstract

Mesoscale model forecasts were carried out beginning at 0000 UTC 19 August for simulating Tropical Disturbance 4, which was named Tropical Storm Debby on 22 August 2006. The Weather Research and Forecasting model, with 25-km grid spacing and an inner nested domain of 5-km grid spacing, was used. The development of a small closed vortex at approximately 0600 UTC 20 August 2006 at 850 hPa was found off the coast of Guinea in agreement with satellite images in the 5-km simulation. Intense convection offshore and over the Guinea Highlands during the morning of 20 August 2006 led to the production of a vortex formation by 1400 UTC at 700 hPa. Sensitivity tests show that the Guinea Highlands play an important role in modulating the impinging westerly flow, in which low-level flow deflections (i.e., northward turning) enhance the cyclonic circulation of the vortex formation. Yet, the moist air can be transported by the northward deflection flow from lower latitudes to support the development of mesoscale convective systems (MCSs). Although the model forecast is not perfect, it demonstrates the predictability of the formation and development of the tropical disturbance associated with the Guinea Highlands.

Corresponding author address: Dr. Sen Chiao, Dept. of Marine and Environmental Systems, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901. Email: schiao@fit.edu

This article included in the West African Weather Prediction and Predictability special collection.

Abstract

Mesoscale model forecasts were carried out beginning at 0000 UTC 19 August for simulating Tropical Disturbance 4, which was named Tropical Storm Debby on 22 August 2006. The Weather Research and Forecasting model, with 25-km grid spacing and an inner nested domain of 5-km grid spacing, was used. The development of a small closed vortex at approximately 0600 UTC 20 August 2006 at 850 hPa was found off the coast of Guinea in agreement with satellite images in the 5-km simulation. Intense convection offshore and over the Guinea Highlands during the morning of 20 August 2006 led to the production of a vortex formation by 1400 UTC at 700 hPa. Sensitivity tests show that the Guinea Highlands play an important role in modulating the impinging westerly flow, in which low-level flow deflections (i.e., northward turning) enhance the cyclonic circulation of the vortex formation. Yet, the moist air can be transported by the northward deflection flow from lower latitudes to support the development of mesoscale convective systems (MCSs). Although the model forecast is not perfect, it demonstrates the predictability of the formation and development of the tropical disturbance associated with the Guinea Highlands.

Corresponding author address: Dr. Sen Chiao, Dept. of Marine and Environmental Systems, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901. Email: schiao@fit.edu

This article included in the West African Weather Prediction and Predictability special collection.

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