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5/31/2021 5:37 am  #1

GFS Vs. NAM Vs. HRRR Vs. ICON - Who Was The Best Offshore California?

=21pxWhich GRIB file do you usually trust the most when sailing offshore southern California?
Check out a recent analysis from a customer's offshore training session. The boat shared their analysis of weather forecast GRIB files on their journey from San Diego out to the synoptic pressure and back over a day and half of sailing approximately 300 miles.

        Model Accuracy is a critical piece of onboard software which can help navigators learn which weather forecast model is performing the most accurate, and provide calibration trends withinin your routing software. Knowing the trend errors are critical to apply within Expedition routing software to ensure you are always routing with the most accurate GRIB file possible!
        This analysis can be done real time while onboard to make better navigating decisions off the best performing weather forecast GRIB file!https://mcusercontent.com/22e50c8be612e64f96a555342/images/57d0b14a-f049-cd15-1124-55bf7f43935b.png
Model Accuracy % - the closer the performance line of the GRIB to the top of the graph the better. Here you can see none of the GRIBS correctly forecast the wind shadow behind the Island San Clemente, and once out into the synoptic pressure the SailDocs GFS was the clear winner!https://mcusercontent.com/22e50c8be612e64f96a555342/images/ce24038d-a529-211d-d3ef-cf1430dd59c9.png
TWS Knots Plot - The thin black line is the boat instrument data for TWS. You can see only the HRRR correctly forecast the lee of San Clemente Island, but then the HRRR over predicted the TWS forecast once out in the significant pressure of the syncopic breeze. Once offshore, the GFS and NAM were the most accurate!https://mcusercontent.com/22e50c8be612e64f96a555342/images/5cc8128e-fc0f-bc65-d803-5ade1597d601.png
TWS Error Knots - here one can see the NAM Model did the best job with a near zero error in its prediction once the boat entered the synoptic around 1000Z UTC. https://mcusercontent.com/22e50c8be612e64f96a555342/images/ba532f32-0426-7352-4f9e-ba2c2223a275.png
TWD Degree Plot - here we can see the HRRR captured the lee behind San Clemente around 0300Z UTC, but then was too far right once out in the synoptic pressure. GFS had the best TWD forecast!https://mcusercontent.com/22e50c8be612e64f96a555342/images/776a0c6a-0f62-c627-b495-b5c88be4c0bd.png
Overall, it was a 3-way tie for top ranking between NO_ GFS, NO_NAM, and SD_GFS. 

HRRR started strong in the littoral environment near San Diego and San Clemente, but failed to be as accurate as the legacy models GFS once out in the syncopic pressure. 

Its critical to know that the HRRR performs well inside the trade winds and synoptic environments, and that GFS and NAM are still winners once offshore! 

The calibrations produced from Model Accuracy suggest minor TWD and TWS adjustments for routing calibrations inside Expedition sailing software.  


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