Danger at Sea: Diagnosing and Communicating the Threat for Strong Maritime Thunderstorms

The National Weather Service's Ocean Prediction Center (OPC) and the Tropical Analysis and Forecast Branch (TAFB) at the National Hurricane Center (NHC) forecast maritime thunderstorms in “offshore zones” year round. These thunderstorms pose daily threats to mariners that traverse the Atlantic waters off the U.S. East Coast, the Gulf of Mexico, and the Caribbean. GPS, an accurate navigation tool, and weather prediction of general wind and wave conditions have allowed recreational boaters to travel farther offshore to fish or sail in smaller boats. The offshore oil industry operates platforms and support vessels of all sizes in the very active convective areas of the Gulf of Mexico. A broad variety of marine activities are vulnerable to strong winds, building seas, and reduced visibility associated with strong convective storms. Often mariners must head in shore, toward approaching storms, to seek safe haven.

To begin to address the challenges of improving the short term prediction of thunderstorms, the OPC and TAFB have identified offshore convective storms as a focus area of the Satellite Proving Ground. A variety of convection targeted proxy products are being evaluated for operational application in preparation for GOES-R and the increased temporal sampling, imager, derived products, and Geostationary Lightning Mapper (GLM).

To better understand the behavior of convective activity offshore and assess the potential capabilities GOES-R will yield, several cases were chosen for evaluation. During summer 2013, a U.S. Coast Guard Academy intern analyzed three significant mesoscale convective systems (MCSs) that affected the Atlantic and Gulf of Mexico offshore forecast zones. Storm behavior in these case studies was characterized using GOES-R proxy products (i.e., the overshooting top detection (OTD) and Vaisala GLD-360 lightning density products) along with surface observations and additional remote sensed wind data from scatterometers. This presentation will focus on convective events that affected OPC and TAFB operations. The results of this research and assessment of the GOES-R proxy products will assist marine forecasters at OPC and TAFB to understand the future capabilities in the GOES-R era and the information to plan and prepare appropriate products to help mariners anticipate and avoid severe weather at sea.