Extreme Maritime Weather—Operational Forecasting Challenges

Marine forecasters of the NOAA Ocean Prediction Center are responsible for warning and forecast services for the western north Atlantic and central and eastern north Pacific Oceans. These waters contain the major storm tracks, great circle shipping routes between North and Central America and Asia and Europe, and fishing grounds of the Bering Sea and northwest Atlantic. WMO standards for marine weather services require wind warnings for existing or anticipated winds of gale (Beaufort Force 8,9), storm (Force 10,11), or hurricane force (Beaufort 12). Over the mid- and high latitude oceans the weather can be extremely volatile, producing numerous, rapidly moving, and explosively intensifying cyclones. Some of these cyclones can become extreme and reach hurricane force intensity. Predicting such conditions is just one of many challenges faced by national weather services tasked with warning and forecast services for the mid- and high-latitude oceans.

The ocean areas are still relatively void, as compared to land areas, of verifying observations of critical meteorological parameters such as pressure, wind speed and direction, and wave characteristics. Forecasters have a growing reliance on remotely sensed vector winds and wave heights from satellite scatterometers and altimeters. Even with such sophisticated instruments, coverage is limited with large temporal gaps between passes, and retrieved winds and waves are only representative of phenomena averaged over a relatively large footprint.

Geostationary satellite imagery and products have improved such that forecasters are now able to see smaller scale cyclones that can meet warning criteria and are short lived. Increased resolution of numerical models and more frequent time steps have placed an added burden on forecasters as, in essence, there is more weather to deal in an allotted shift and predictive window. Both of these issues are very beneficial but require added time to address properly.

The Global Maritime Distress and Safety System required High Seas bulletins are the principal method for communicating hazardous weather. These bulletins are often lengthy and require deciphering by the mariner. Traditional weather graphics designed for black and white transmission via High Frequency radiofacsimile are limited for conveying the breadth of conditions associated with mid-latitude cyclones.

This talk will discuss the challenges faced by weather services that provide marine weather warning and forecast services over large and active ocean areas and discuss activities to address these challenges.