What's the Probability? Weather Rock Stars Convene.

Posted by Darrell Nicholson with Ralph Naranjo at 12:25PM - Comments: (9)

The bright red colored regions on this wind speed forecast chart indicate regions where the sustained wind velocity has a 90 percent probability of being 15 knots or greater.

A changing climate brings changes in the frequency and intensity of extreme weather events in Atlantic and Pacific basin, another reason to hone your forecasting skills and become familiar with all the meteorological tools readily available to the public.

In the May 2017 issue, PS Technical Editor Ralph Naranjo explored the latest marine forecasting technology used by meteorologists and described how sailors put these forecasts to use. Early next month Ralph and some of the most  prominent marine weather experts will be diving deeper into the topic of reading the weather during a one-day symposium. Hosted by the Cruising Club of America , the event is set for Feb. 10 with all proceeds going to advance sailing safety training and research. More details about the event appear at the bottom of this story.

A recent addition to the marine forecaster's toolbox is probablistic wind speed guidance  disseminated by the Ocean Prediction Center (OPC). The forecasts take the available weather data and graphically present them in an easy-to-understand weather map.The above chart shows an example of the OPC's experimental wind probability charts. The bright red colored regions on the pictured chart indicate areas where the sustained wind velocity has a 90 percent probability of being 15 knots or greater. Other shades of color indicate lower probability of the current wind conditions being 15 knots or greater. There are also two other similar charts, one showing the probability of wind speeds of 25 knots or greater and another indicating regions that are likely to experience 35-knot winds or greater.

These charts are generated using model data derived from the Global Ensemble Forecast System (GEFS)—a statistical process that compares likely deviations from model assumptions and delivers a midrange solution. These forecasts differ from more traditional deterministic weather reports by the addition of a percentage based "how likely" component.

These maps also display the location of high and low pressure centers and include isobars with the usual 4 millibar spacing. A user in the northern hemisphere can determine wind direction by recognizing that wind flows counterclockwise around lows and curve inward and diverge from the isobars at about 20 degrees. Around highs, wind flows clockwise at a 20 degree outward deviation to the isobars.

If you are intrigued by probabilistic forecasts and other new advances in marine forecasting for sailors, then mark your calendars for February 10. On Saturday, February 10 at the Marine Institute of Technology and Graduate Studies in Linthicum Heights, MD (right next to the Baltimore Washington International Airport), PS Technical Editor will be joining a team of marine weather experts to bring sailors up to date on the most current forecasting products and techniques. Deadline for registration for the one day symposium, hosted by the Cruising Club of America, is Feb. 5.

Here’s the agenda for the day long event:

  • Marine Weather Fundamentals, mid-latitude, tropical, extratropical conditions (Ken McKinley, Locus Weather); - 500 mb conditions –significance and analysis (Lee Chesneau – Chesneau Marine Weather)
  • Ocean currents, waves, and sea state (Frank Bohlen, University of Connecticut Marine Sciences )
  • Forecasts and forecasting (Joseph Sienkiewicz– NWS OPC, Ken Campbell – Commanders Weather)
  • Communications VHF to Inmarsat (Jim Corenman)
  • The Role of the Navigator – Information processing and routing (Stan Honey, Ralph Naranjo) - Questions from floor - Roundtable Discussion (With all presenters)

 For more information visit the Cruising Club of America’s website for the event https://sas.cruisingclub.org/course/wx18.

For more on the impacts of climate change on extreme weather, see the 2012 IPCC Report Managing the Risks of Extreme Weather Events and Disasters to Advance Climate Change.
It is worth noting that "extreme" weather is not limited to tropical storms, and includes extra-tropical activity, El Nino events, etc. that can have impact on global cruising.

There is also the recent report by the National Atmospheric and Oceanic Adminstration's Geophysical Fluid Dynamics Lab on Global Warming and Hurricanes. The report notes pronounced upward trend in the frequency of Atlantic storms during past 140 years. It also reports on a more recent statistical model that indicates little or no increase in the number of hurricanes and tropical storms when researchers apply a statistical model to adjust for "missing storms" (based on the assumption of under-reporting) during the late 19th and early 20th century. 

[1/28/18] This article has been edited for accuracy and to address the global warming brouhaha in the comments section. 

Comments (9)

Thank you for updating the article and citing some scientific sources. Their inclusion adds considerable credibility to the article. Hopefully, readers will read these and other scientific sources and draw their own informed opinions.

Posted by: Trimariner | January 29, 2018 7:20 PM    Report this comment

Please let's keep the climate change denying out of this. The consensus amongst objective scientists (ie. ones not working for the energy sector or trying to keep or get a job with the current administration) is that climate change is happening and that humans are affecting this change. Can't we all just be sailors who, by our very nature, must learn to adapt to changing circumstances and keep the ideology out of it? S/V Kristy's comment is helpful - where can we get the information provided at the seminar if we'd rather be someplace warm on our boats?

Posted by: Gene %26 Molly | January 28, 2018 5:22 PM    Report this comment

This is a really interesting model, but as the first commentor noted, there's absolutely NOTHING in this article to support the article's title or opening assertion that climate change is generating more extreme weather events. Has this model been back-checked over the last 100 years to compare its output to historical records of extreme weather events? Has that analysis corrected for the more accurate tracking of extreme weather events in recent years, particularly over the open oceans? Has the model then beeen used to project the likelihood of extreme weather events given various climate change forecasts? If so, what is the margin of error, given the aforementioned comparison vs. historical data? If climate change scientists want to be taken seriously, they need to do the actual research, instead of just publishing pretty pictures and bald assertions. This model is only a tool in that research. A research tool a conclusion.

Posted by: rmfii | January 28, 2018 12:22 PM    Report this comment

The article made the statement, "Climate change is bringing more extreme weather events to both the Atlantic and Pacific basins," Where is the data to substantiate this assertion? Without rigorous scientific study, the statement has little validity.

Posted by: Trimariner | January 28, 2018 9:24 AM    Report this comment

Kudos. This is great! Future west coast lications?

Posted by: CA Dude | January 26, 2018 7:31 PM    Report this comment

I'm really pleased to see this sort of seminar is happening and weather rock stars are convening. Is there any chance a movement can be started that replaces the archaic one-color isobar charts that have been used for decades and a far more user friendly version be invented that applies in the 21st century? I know the value of the existing charts is that they are evaluated by a professional meteorologist who hand draws a lot of the content putting reliable experience and intelligence behind the atmospheric facts. That's good and it doesn't have to stop. I'm grateful for it. I can read them, but they frustrate the heck out of me because they could be so much better. The tools to do it, even "hand drawing", are readily available and cheap.

It's time to abandon the "weather fax" constraints and get on with a digitized, color, easy-for-anyone-to-read weather chart.


Posted by: Jovini | January 25, 2018 4:09 PM    Report this comment

How can we get printed content or other seminar locations in the future?

Posted by: Catalina 42 | January 25, 2018 2:38 PM    Report this comment

Many... no, most of us will not be able to attend. Can this be made available on line for viewing at a later date?

Posted by: S/V Kristy | January 25, 2018 2:37 PM    Report this comment

The link to the Cruising Club site for registration to the Weather seminar does not work.

Posted by: CRAB | January 25, 2018 9:37 AM    Report this comment

New to Practical Sailor?
Register for Free!

Already Registered?
Log In