18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Thursday, 2 August 2001
Satellite Applications for Tropical Wave/Tropical Cyclone Tracking
Jason P. Dunion, NOAA/AOML/HRD, Miami, FL; and C. S. Velden and J. R. Rhome
African easterly waves (often referred to as tropical waves) are one of the primary seedlings for Atlantic tropical cyclone development as well as being sources of localized heavy rains and squall conditions to tropical islands. Easterly waves move off the coast of Africa and propagate westward across the Atlantic, Caribbean, and portions of the east Pacific. Locating and tracking these waves remains a difficult challenge in tropical analysis and forecasting due to the lack of observations over the tropical oceans. Moreover, interactions with larger scale synoptic flow often mask or distort their appearance in satellite imagery. Traditionally, westward moving organized areas of clouds/convection are tracked in the absence of observed data. However, this technique is often flawed in cases when the wave axis is displaced from the convection or when the convection is being caused by another atmospheric feature altogether. Properly locating and analyzing these waves and associated weather represents a vital step in the forecast process. It is therefore necessary to develop analysis tools that aid in locating these features.

Recent collaborative efforts between NOAA's Hurricane Research Division (HRD) and the Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS) have resulted in the development of several new satellite-derived products designed for tropical cyclone applications. These products utilize geostationary satellite winds produced at UW-CIMSS which are made available in real-time.

Low-level cloud-drift winds produced from the high-resolution visible channel on GOES -8/10 and GMS-5 are generated and adjusted to the surface using a combination of HRD's planetary boundary layer model and empirical optimizations derived from comparisons with in situ data in tropical cyclone environments. This allows for the analysis of both low-level and surface wind fields near and peripheral to the circulation center. Shortwave IR cloud-drift winds are currently being developed to compliment the visible winds for nighttime coverage.

Color enhanced 850 hPa relative vorticity products are now being produced in real-time by UW-CIMSS and are available for multiple ocean basins. This product is created from local, high-resolution 3-dimensional objective analyses that are strongly influenced by the assimilation of low-level cloud-drift satellite wind data. To promote its use as a diagnostic tool, the vorticity product is being made available as an animated 5-day java loop. This product has shown potential for use in tropical wave tracking as well as for examining interactions between environment features such as tropical cyclones, tropical waves and mid-latitude fronts.

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