Weather

The following is a summary of some significant tropical synoptics and events which can influence the weather encountered by yachts in the South Pacific. An overriding influence in the tropics and subtropics is the Subtropical Jet (SJT). It’s a semi-permanent feature near the poleward margin of the tropics and its strong baroclinic field, especially in winter, can and does supply energy for weather disturbances in low latitudes.

A Tropical Cyclone in the SW Pacific is a cyclonic warm core system with winds of 34 knots or greater, whereas a Hurricane or Typhoon has winds of 64 knots or greater. BoM rates tropical cyclones (TC) by a scale of 1 to 5. This scale was established for local conditions and is similar to the Saffir Simpson Scale used in much of the world.

The MJO or Madden- Julien Oscillation is a wave oscillation travelling eastward around the globe on an average of 40 days. When the wave is over the western tropical Pacific heavy convective activity is initiated.

The following is a series of lectures I have given to yachties with the aim to provide a bit of information on weather terminology, definitions, rules of thumb and the use of Grib files for forecasting. These papers are not technical and are designed to help the user wade through the sometimes confusing terminology from various forecasting sources and also to provide some hints as to how to best use data obtained from the Gribs.