Weather - Ocean Navigator

15 Feb

Weather scales

Ocean NavigatorWeatherfronts, marine weather, Rossby waves

Ocean voyagers have to be aware of many factors when it comes to ocean weather. Among these factors are the various scales at which the atmosphere operates. To the experienced observer, the observation of wave-like characteristics in the atmosphere is second nature. The observer sees the wave-like patterns in the clouds or the pulsating nature of snowfall as simple manifestations of these characteristics. The atmosphere exhibits wave-like properties because its essential nature is that of a fluid. And, as with any fluid, waves are produced in the atmosphere when it is disturbed. These waves come in all sizes. Indeed it…

20 Dec

Weather window for crossing the Drake Passage

Ken McKinleyWeatherAntarctic Peninsula, Antarctica, Drake Passage, sea ice, Southern Ocean, weather

In the northern hemisphere as we move toward the winter solstice, our counterparts in the southern hemisphere are approaching their summer solstice with the longest day of the year on the way. At the highest latitudes of the southern hemisphere, this is the time of year when ocean voyages are possible. In particular, it is possible to get to Antarctica, and there has been an increase in both commercial and recreational passages in this part of the world in recent years. Even at this time of the year, though, passages in these areas come with significant risks. In fact, a…

12 Oct

Rocks in the Pond

Ken McKinleyWeatherduration, fetch, waves, weather, wind speed

Almost everyone is familiar with what happens when one tosses a small rock into a calm pond. The rock displaces the water level where it impacts the pond, and as the water level rebounds toward the equilibrium level, waves are generated which propagate away from the point of impact in concentric circles. This is a manifestation of the energy that the rock imparted to the surface of the water. A similar phenomena applies when tossing a small rock into the ocean, but the difference is that most of the time, the ocean is not calm, and waves already exist. In…

15 Aug

Dogwood and Cactus

Ken McKinleyCrew's Picks, Uncategorized, Weatherweather

The title might suggest that this newsletter will be about flowering trees and desert succulents. Rather, the title refers to two new supercomputers that NOAA placed into service in late June of 2022. These computers are twins, meaning that they have nearly identical capabilities so that when one needs to be taken down for maintenance or upgrades, there is no loss of operational capability. They are located in separate parts of the country, again, allowing for redundancy in the case of some sort of an issue at one of the sites. They are some of the fastest computers in the…

28 Jun

Solstice weather charts

Ken McKinleyHome Page Hero, Weather48 hour chart, 48 hour forecast, Atlantic surface forecast, highs, isobars, lows, NOAA, NWS, Pacific surface forecast, sea ice, troughs, weather, weather charts, weather fax, wind, wind direction, wind speed

For this newsletter, I thought it might be a good idea to look at a few surface forecast charts and go through the features of the charts. This has been done before, but it is always good to have a refresher for this material, and there have been a few changes in the charts in recent years. Then I realized that we have just passed the summer solstice in the northern hemisphere, so it made sense to look at some charts produced on the summer solstice, and also to look back at the same charts produced on the winter solstice…

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…