What’s the Probability? Weather Rock Stars Convene.


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 technologyused 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.

Heres 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 Americas 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 amore 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.


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