“Once upon a time, people identified the god Neptune as the source of storms at sea. Today we call these storms hurricanes … The only people who still call hurricanes acts of God are the people who write insurance forms.” ~ Neil De Grasse Tyson
Speaking of “acts of God,” we had an earthquake Tuesday evening. With a magnitude of 4.4, it was just enough to get our attention, although I was in the yard watering and missed it. Oh well, there will be a next time!
Weather-wise, we’ve been blessed with an uncommon, late summer cool-down. Daytime temperatures have lingered in low 80s, with nights dropping into the 60s. Don’t be fooled – there is more summer heat to come before we’re swept away by autumn winds.
The recent hurricane in Hawaii brought to mind the terms used for wind measurement miles-per-hour and knots. In meteorology (and sea and air navigation), a knot is a unit of speed typically used to indicate wind speed. Mathematically, one knot is comparable to 1.15 miles per hour. As a general rule in the U.S., wind speeds over land are expressed in miles per hour, while those over water are expressed in knots (largely because knots were invented over a water surface). Since meteorologists deal with winds over both surfaces, they adopted knots for consistency. However, when passing along wind information to public forecasts, knots are typically converted into miles per hour for the public’s ease of understanding. Thank you!
The reason sea winds are measured in knots is because of century-old maritime tradition. In centuries past, sailors didn’t have GPS or speedometers to measure their speed across the open sea. So, to estimate the ship’s speed, they crafted a tool of a rope several nautical miles (1.1508 mi) in length with knots tied at intervals along it and a piece of wood tied at one end. As the ship sailed along, the wood end of the rope was dropped overboard into the water, where it remained roughly in place as the ship sailed away. The number of knots was counted as they slipped off the ship out to sea over 30 seconds (timed using a glass timer). By counting the number of knots that unspooled within that 30-second period, the ship’s speed could be estimated. How ingenious is that?
The weekend forecast is for above-average temperatures. An atmospheric disturbance over the Gulf of Alaska next week may bring cooler and cloudier weather.
Weather – like life – can often be unsettled and uncertain or “up in the air.”
Sue Kilpatrick is a Crescenta Valley resident and Official Skywarn Spotter for the National Weather Service. Reach her at firstname.lastname@example.org.