When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather today: for the sky is red and lowering.(Matthew 16.2-3)
To the sailor, the above bit of Biblical weather advice is better known in the following rhyme:
“A red sky in the morning, sailors take warning; A red sky at night is a sailor’s delight.”
For millennia, intelligent sailors have been trying to forecast the weather by the appearance of the sky and cloud formations, in conjunction with fluctuations in wind speed and direction. This knowledge was codified in simple rhymes and passed on to generations of apprentice seamen.
By the beginning of the 19th century, new sailors were still learning many weather rhymes to help them make correct choices at sea — everything from what sail combinations their vessel should be carrying for expected weather conditions, to when a pump watch should be set — as evidenced by the following rhymes: “When rain comes before the wind, halyard, sheets and braces mind. When wind comes before the rain, soon you may make sail again,” and, “When the porpoise jumps, stand by your pumps.”
But a technical revolution was taking place in weather prediction between the beginning and end of the 19th century, and this revolution began to show up in modernized weather rhymes: “At sea with low and falling glass, soundly sleeps the careless ass. Only when it’s high and rising truly rests a careful wise one.”
The glass referred to above was of course the glass-tube mercury barometer, a tool that, when combined with his well-worn weather wit, might forewarn a seaman of future foul weather. But it was the development of the radical new aneroid barometer in 1844 that gave seamen a more valuable weather instrument. The word “aneroid,” derived from Greek words meaning “not of fluid form” was touted by Capt. Lecky, in his massive, 777-page book, Wrinkles in Practical Navigation (1881). He noted that the aneroid barometer “is by far the better instrument for use afloat. It is more portable, and occupies much less room … and is more sensitive than the mercurial barometer, and at all times — more especially in heavy weather — easier to read.”
Since it was more accurate and much easier to read, it became possible for very minute changes in pressure to be more readily detected by the observant captain reading his aneroid barometer’s finely divided analog scale. He began to notice that small changes in pressure seemed always to occur when his ship tacked, and he soon learned that in the Northern Hemisphere (in all wind conditions except near the equator), tacking to starboard would take his ship toward a higher barometer, while tacking to port would take it toward a lower barometer.
By the end of the 19th century, some of the complicated weather mechanisms driving storm (and specifically hurricane) formation and track were beginning to be better understood, thanks to the aneroid barometer. The U.S. Navy’s Hydrographic Office Publication #86 (1901) offered the following non-rhyming recommendations to masters using aneroid barometers (based on decades of logged information) for preparing a vessel ahead of an approaching hurricane:
“A vessel suspecting the dangerous proximity of a hurricane should lie-to for a time on the starboard tack to locate the center by observing shifts of the wind and the behavior of the barometer. If the former holds steady and increases in force, while the latter falls rapidly, say at a rate greater than 0.03 inches per hour, the vessel is probably on the track of the storm.”
But even with such a valuable and growing body of scientific weather knowledge available at the close of the 18th century, some seamen still chose to fall back on the security of those bad poetic musings for guidance in certain waters. One humorous, if pessimistic, example is an Irish variation on that old jingle for remembering the number of days in each month, but relates directly to the weather a seaman might expect to encounter near the coasts of Ireland — barometer be damned:
“Dirty days hath September, April, June and November. From January up to May, the rain it cometh every day. All the rest have thirty-one without a blessed gleam of sun; and if any of them had two and thirty, they’d be just as wet and twice as dirty.”