I still have some lecture notes on hurricanes to which I have added some notes based on personal experience. The lecture was given by a hurricane expert from the Dutch Weather Office with the nick name ‘Hurricane Peter’ who was the expert there on the subject of hurricanes. He sailed earlier as a mate on ships during which time he developed an interest in hurricanes since he once ended up in one in which he almost died.
The situation in the Atlantic was not difficult, we received the rather accurate hurricane positions via radio weather reports from the USCG stations. It was different when we had to cross the Pacific, information was more scarce and tended to be less accurate. Here it paid off to be on your toes for certain signs as outlined below.
Tropical cyclones are often preceded by a day with an uncommon brightness and remarkable good visibility. The atmosphere is often oppressive. These conditions are then followed by an extensive cirrus cloud, in the form of converging bands pointing in the direction of the storm center (radiating cirrus). In that direction the cirrus bands then merge closer to the horizon into a smooth cirrostratus deck with flaming sunrise and sunset.
If you are on a westerly course to the Caribbean and you see these clouds behind you at sunrise, then you better be very careful. Ten against one that there is a warning about a tropical storm at hand.
The average air pressure for the hurricane area you are in is found in the pilots and on the pilot charts. If this average air pressure deviates from the standard deviation for the date after interpolation, then there is a chance of a hurricane and you have to pay close attention to the other signs, especially a deviating sea course and swell and above all the clouds. Long before the heavy cloud bank of the hurricane body appears above the horizon, you see apparently radiant cirrus clouds. In my days we didn’t have the luxury of a barograph which is a helpful instrument when sailing in a hurricane area. However, we noted the airpressure every hour, sometimes even more often.
As said one of the surest announcements of an approaching tropical cyclone is a more than normal deviation from the air pressure below normal, for example more than 3 hPa below the normal value for that position (corrected for the daily course). It is then important to keep the barometer reading regularly. If the deviation continues to increase, it is likely that the ship is approaching the cyclone at that rate. If the corrected deviation is more than 5 hPa, the cyclone is probably within a distance of 170 nautical miles.
Any wind that deviates from the normal condition, both in direction and force, may indicate a malfunction. There may be a reinforced or a weakened trade wind.
If swell waves come from a different direction than normal for that position, that may indicate the presence of a cyclone. The seaway, generated by the wind field of the storm, after leaving that wind field changes into swell with longer and lower waves. These waves propagate in all directions at a speed that is greater than the speed of movement of the cyclone in its trajectory. Normally the wave period is 4-7 seconds. If an abnormal swell is observed with a much longer period, e.g. 15-20 seconds, then this is a strong indication of the presence of a tropical cyclone.
On the north latitude, the right front quadrant, and on the south latitude, the left front quadrant, is called the “dangerous quadrant.” In those quadrants, the wind moves the ship towards the orbit of the cyclone, and runs the risk of getting into the center of the hurricane.
If one knows globally the bearing of the center, an attempt can be made to find out in which quadrant of the tropical cyclone one is. In general, a falling air pressure will be observed in the front half of the cyclone and a rising air pressure in the back half. By now paying attention to changes in wind direction, it is possible to determine which quadrant you are in.
In the right half, a stationary observer, on both the north and south latitude, will experience a veering wind, and in the left half a backing wind (vice versa if the ship moves faster in the trajectory direction than the eye of the cyclone) .
So when (in the northern hemisphere) a falling air pressure is observed together with a veering wind, the ship is in the dangerous quadrant, or the dangerous quadrant is approaching the ship. In the southern hemisphere a falling pressure and a backing wind is observed in the dangerous quadrant.
In the dangerous quadrant the ship is driven by the wind to the orbit of the cyclone and will have to be sailed into the wind. It is best to sail at the highest possible speed with the wind in 2 or 3 regions from the front (in the northern hemisphere on the starboard side, in the southern hemisphere on the port side). In the right half, a stationary observer, on both the north and south latitude, will experience a circulating wind that is therefore broadly blowing, and in the left half a circulating wind will therefore shrink (vice versa if the ship moves faster in the trajectory direction than the eye of the cyclone) .
So when (in the northern hemisphere) a falling air pressure is observed together with a blowing wind, the ship is in the dangerous quadrant, or the dangerous quadrant is approaching the ship. In the southern hemisphere a falling pressure and a shrinking wind is observed in the dangerous quadrant.
In the dangerous quadrant the ship is driven by the wind to the orbit of the cyclone. To escape the ship will have to sail into the wind. It is best to sail at the highest possible speed with the wind in 2 or 3 compass points from the front (in the northern hemisphere on the starboard side, in the southern hemisphere on the port side).
The following is from the NOAA’s Mariner’s Guide For Hurricane Awareness In The North Atlantic Basin.
Vessel at A: put wind at 160° relative to the ship on the starboard side making best course and speed into the left semi-circle of the system. Vessel at RF and RR: put the wind at 045° relative to the ship on the starboard side attempting to make best course & speed to clear the system.
NOTE: Wind and seas in the area of RF and RR may result in drastically reduced forward speeds of a ship attempting to open from the tropical cyclone. Vessel at LF & LR: put the wind at 135° relative to the ship on the starboard side making best course and speed to increase separation between ship and tropical cyclone.