Weather - Ocean Navigator

27 Apr

Using radar offshore to detect squalls

Robert MacFarlaneWeather

In 2003 I installed a radar on my 1983 Morgan N/M 456, Tiger Beetle, to help with singlehanded races between San Francisco and Hawaii. The Furuno 4 kilowatt 24-inch radome I went with was one of the better small boat radars. The 24-inch-wide antenna provided better angular resolution than an 18-inch antenna, the 4 kilowatt power punched well through rain, and it had a guard zone/sleep feature to conserve power. I would set up the guard zone on the black and white display and targets that entered the guard zone would sound an alarm so I could check the target. I…

14 Apr

Atmospheric ridges and troughs

Ocean NavigatorWeather

The formation of ridges and troughs in the atmosphere has important effects on weather at sea. Here is a look at ridge and trough structures and how they can influence surface low pressure zones and precipitation. Distinctive cloud shapes form in the vicinity of the jet stream and are dependent on the extent of both horizontal and vertical mixing of warm, moist air and cold, dry air. The amplitude and width of ridges and troughs directly influence cloud shape and also indicate surface weather feature development. High-amplitude troughs tend to pull large amounts of cold, dry air south into regions…

09 Feb

Using satellite images

Ocean NavigatorNewsletter, Weather

Satellite imagery provides a great deal of information on past, present, and future weather. Each cloud swirl, streak, and puff can be associated with a particular weather system or phenomenon. And when images are viewed by a trained voyager with a good understanding of weather dynamics, routing and course decisions can be made with confidence. The most important weather element that satellite imagery provides to the voyager is cloud data. Analysis of cloud altitude, shape, and movement goes a long way toward painting what the associated air mass is doing. Clouds are categorized by both their height and shape, with…

31 Dec

Weather models and GRIB files

Peter IslerShort Tacks, Weather

Weather models and their digitized end product, the GRIB file, are key facets of weather forecasting. An understanding of these elements will help any voyaging sailor to better decipher the weather. When I was in college, I was primarily a dinghy sailor and was just getting started in offshore navigation and race tactics. I knew how to read a weather map and listen to the marine forecast on the VHF radio, but beyond that I just took what Mother Nature gave me. In college, I majored in meteorology since it was the closest subject I could find to my favorite…

16 Dec

Weather, December 2021

Ken McKinelyWeather

My friend and weather colleague Lee Chesneau passed away on Thanksgiving Day 2021, almost exactly three years after he suffered a massive stroke. As a weather forecaster, instructor and as a person, Lee was one of a kind and mariners continue to benefit from his work. I was first introduced to Lee more than 20 years ago when we worked together providing a two-day weather course for the Ocean Navigator School of Seamanship. At the time, Lee was working as a senior forecaster for what was then known as the NOAA’s Marine Prediction Center, now known as the Ocean Prediction…

13 Oct

Weather, October 2021

Ken McKinleyNewsletter, Weather

Sometimes we just need to laugh. Dealing with the global pandemic over the past year and a half has been tough on all of us. On top of this, the past two Atlantic hurricane seasons (this one is not quite over yet) have been extremely active and have resulted in significant property damage and destruction that has seriously impacted the lives of many people. Unfortunately, there have also been many injuries and fatalities associated with sone of these storms. The forecasters at the U.S. National Hurricane Center have done a great job providing timely and accurate forecast information for the…

01 Sep

Cooking up a cyclone

Ocean NavigatorWeatherENSO, hurricanes, marine weather, tropical cyclone development, tropical cyclones, wind shear

As the June to November hurricane season evolves, attention will gradually focus on certain conditions of both atmosphere and ocean — six specific factors, or “ingredients.” Not only are these factors necessary, but their timing needs to be synchronized to cook up a cyclone. A number of those “ingredients” can be affected by the status of ENSO, a known, periodic, irregular (two to seven year cycle), tropical climactic seesaw of atmospheric pressure, sea surface temperature and winds. Finally, an unanticipated factor may appear that warps model predictions of a potential storm’s genesis, intensity and track – an effect sometimes dubbed…

01 Sep

Crossing the Doldrums

Ocean NavigatorOcean Voyaging, WeatherAscension Island, Barbados, Galapagos, GRIB files, Hawaii, ITCZ, Marquesas, ocean sailing, offshore sailing, The Doldrums, trade winds, Tuamotus

For centuries sailors dreaded the aptly named Doldrums. This band of windless, hot, and humid weather near the equator could stall sailing ships for weeks, driving the crew to distraction with the monotony and sometimes even leading to the onset of scurvy as fresh supplies ran out. While sailors today needn’t fear scurvy, most of us still dislike this part of the ocean. Most voyagers try to minimize time spent in the Doldrums. This strategy starts with obtaining accurate weather forecasts, whether over single-sideband radio or satellite phone connection. Even in the last 15 years that I’ve been voyaging, the…

19 Aug

Ken McKinleyNewsletter, Weather

We are now well into the 2021 hurricane season and are watching the evolution of tropical cyclones in the Atlantic and the Pacific. In the past I have used these newsletters to present some information about particularly memorable hurricanes, but this time let’s take a look at a system that, while impactful for some, has not been a historic system by any measure. This system was very slow to develop despite traveling over some rather warm ocean waters at times during the first part of its history. I will examine this system through a series of satellite images with comments…

30 Jun

Tim QueeneyWeather

On March 22, 2021, NOAA announced that the National Weather Service (NWS) would use a new global computer model for weather forecasts. This is an “under the hood” type of improvement that most voyagers won’t see directly. If the new system works as advertised, however, voyagers should see better weather forecasts on their vessels. NOAA says the new Global Forecast System (GFS) “will increase forecast capabilities across the U.S. These advancements will improve hurricane genesis forecasting, modeling for snowfall location, heavy rainfall forecasts, and overall model performance.” The GFS is a numerical weather prediction model that uses a mathematical model…