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Storm Weather Forecasting Improves with High Def Gridded Marine Forecasts

Hugh Cobb, TAFB Chief, showing Terry Boram one of the new HD graphics now available. By Clint Boram
Hugh Cobb, TAFB Chief, showing Terry Boram one of the new HD graphics now available. By Clint Boram

Mariners navigating the offshore waters in the Gulf of Mexico, Caribbean Sea and portions of the tropical and subtropical North Atlantic Ocean have long relied on the Tropical Analysis and Forecast Branch for weather analyses, forecasts and warnings. Over the past four years, TAFB has launched a grassroots effort to configure the Advanced Weather Interactive Processing System (AWIPS) Graphical Forecast Editor (GFE), currently used by local National Weather Service Forecast offices, for their offshore waters forecasting (OFF).

TAFB Branch Chief Hugh Cobb recently discussed the experimental gridded marine forecasts, as well as a revision to the Mariners 1-2-3 Rule.

TAFB, a branch of the National Oceanic and Atmospheric Administration’s National Hurricane Center, has an offshore area of responsibility of 14 million square nautical miles – the largest marine areas of responsibility in the world. Until recently, TAFB had been producing more than 100 products a day using antiquated forecasting procedures. The forecasters’ diverse customer base of pleasure craft owners, fishermen, commercial operators and oil companies relied on these products to keep them out of harm’s way.

The lengthy text forecasts and the low-resolution, 24-hour legacy wind/wave charts displaying fronts, troughs and pressure centers were often confusing and unable to resolve considerable variations in conditions between diverse geographical areas such as east versus west of the Bahama Bank.

Cobb explained that, as part of the transition to the production of gridded marine forecasts in GFE, TAFB’s territory was divided into 32 zones allowing forecasters greater ability to monitor local weather patterns and provide end users with forecasts for specific areas of interest.

Once the GFE software was initialized, forecasters could load model outputs to grids at high spatial and temporal resolutions. Now, surface wind speed/direction, surface wind gusts, significant wave height, and marine hazards are available at a spatial resolution of 10 kilometers, with the initial temporal resolution of six hours out to 144 hours or six days.

Forecasters are using the GFE “Smart Tools” to adjust model output, allowing improvement in local geographical and topographical effects, as well as softening forecast differences between neighboring zones and offices.

“Forecasters are able to manually make adjustments to model data based on their expertise, local knowledge and marine effects,” Cobb explained. With the latest forecast displayed on the GFE, he highlighted a few aspects of the new software’s potential.

Beginning with the official saved forecast, forecasters can now blend two or three global models to produce an ensemble forecast. For example, if over the last six hours the UKMET forecast model proved more consistent with actual observations, the forecaster can then blend that model with the original forecast, giving it a higher weighed value.  Using a brush tool, they are also able to “soften” hard edges in the forecast parameters, providing a better transition between higher and lower winds, wind gusts or seas.

As Cobb demonstrated more of the tools the GFE had to offer, he stated, “The Smart Tools allow for science to better be incorporated into the forecasting process.”

Another new feature that mariners will see this hurricane season is a revision to the Mariners 1-2-3 Rule, or Danger Rule. This rule assumes an average forecast track error of 100-200-300 nm at 24-48-72 hours, respectively, creating a large avoidance area for mariners. Cobb said that this “over-warned” cone was forcing many of their legacy customers, such as freighters, to divert over large areas, costing them lost time and revenue.

The new calculation for the experimental Tropical Cyclone Danger Graphic includes historical track and intensity errors, whether the alternative track crosses over land or water, the size of the cyclone at the start and the typical changes it could make as it strengthens and moves forward.

The result is the probability of actually experiencing certain wind speeds. The new avoidance swath will display a 5 percent, 34-knot wind speed probability, representing low to medium risk, denoted within a dashed line and a 50 percent 34-knot wind speed probability denoted with a solid line representing a high risk of tropical force winds.

“Educating our current and new customers is key in the success of this program,” Cobb emphasized.

Comments and feedback are highly encouraged. For more information or to provide feedback, go to: www.nhc.noaa.gov/marine/grids.php.
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DOWNLOAD FORECASTS
The TAFB experimental gridded forecasts are available in the National Digital Forecast Database (NDFD).  Mariners can access them via: Gridded Binary Version 2 (GRIB2) files via Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP).

Extensible Markup Language (XML) via Simple Object Access Protocol (SOAP).

Graphics via web browser: www.nhc.noaa.gov/marine/grids.php

Terry Boram simply enjoys being around the water. Whether it’s sailing with her husband on their 34-foot trimaran, kayaking, SUP or walking the beach, she always finds something fun to write about.

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