Are you familiar with katabatic winds?

Its a brief overview of three nasty “descending” winds affecting mariners and treats the phenomenon called katabatic wind and discusses some specific katabatic winds a little more into detail and how they can affect both seafarers and landlubbers.
Briefly, the katabatic wind is downslope gravitational flow of colder and denser air, beneath relatively lighter and warmer air, that rather suddenly can reach high wind speeds.
 

The katabatic wind

This post will deal with a type of wind called the katabatic wind, which comes from the Ancient Greek word katabasis meaning “descending”.
The katabatic wind is a drainage wind that occurs when the air flowing downslope from a high elevation of a mountain, plateau, and hill cools more than the air in the surrounding atmosphere.
Cold air is, as many of you probably already know, heavier than warm air. As a result of that, a thermal high pressure is formed over the mountain range while the air pressure in the surrounding atmosphere is relatively lower.

There are different kinds of katabatic winds, determined depending on where they flow and how they form. For example, the Santa Ana in southern California, the Böhmwind in the Ore Mountains along the border between the Czech Republic and Germany, the Oroshi in Japan and the Williwaw found for example in the Strait of Magellan (southern Chile). We will, however, below focus on three other katabatic winds…
 

The Piteraq

The Piteraq is a cold katabatic wind originating on the Greenlandic ice cap or high mountainous plateaus (especially at the small village Tasiilaq), sweeping down the east coast.
The Piteraq is triggered by large low-pressure systems just east or southeast of the Greenlandic coast, possibly resulting in extremely strong and gusty winds near the coasts!
They are most common during the autumn and winter and could typically reach wind speeds of around 100-150 knots.
In 1970, the strongest Piteraq occurred at Tasiilaq, experiencing gusts of more than 160 knots which is stronger than a category 5 Atlantic hurricane! This specific Piteraq resulted in such severe damage to the city, so they subsequently considered closing the town. After this occasion, Tasiilaq created an official warning system just for Piteraqs whereupon an alarm will sound when a Piteraq is forecasted.

The Bora

The Bora is a cold, and usually very dry and often gusty, katabatic wind, flowing from the mountains in Croatia and Slovenia towards the Adriatic Sea.
One can distinguish between the anticyclonic (or white) Bora and the cyclonic (or black) Bora.
The white Bora has a large high-pressure center over Europe and a lower pressure with a not as defined center over the Mediterranean.
The black Bora has a low-pressure center in the southern Adriatic Sea or Ionian Sea, bringing possibly substantial amounts of rain and snow to the region.
Associated with this, the black Bora is also accompanied by low clouds, reduced visibility and rain or drizzle. Especially over open water, these conditions can be very noticeable making it difficult for vessels to pass the area. It is usually in the southern Adriatic Sea where the strongest black Bora winds are usually found.
The Bora usually builds up at a somewhat moderate pace and a continuous Bora with gale-force winds over the Adriatic Sea lasts, on average, about 12 hours, but they can occasionally last up to two days. A Bora that reaches gale force at some point in its existence typically lasts 40 hours, with a maximum of five days.

The Mistral

The Mistral is a cold katabatic north and northwesterly wind, flowing from the Alps and mainly down southern France and the Mediterranean, which strongly affects seafarers!
You can read more about the Mistral here.