The Great Southern Route : 2010 - 2011
WEATHER ROUTING EQUATORIAL AND INDIAN OCEAN 070 | GSR ridges farther west move into the Indian Ocean and eventually merge with the semi-permanent ridge, again, inducing surges of higher E-SE trade winds across much of the region. However, the greatest weather dangers occur as fronts approach and pass farther to the south, particularly in and near Mozambique Channel and much of Madagascar. Post frontal passage S-SW winds can still reach as high as gale force, especially within Mozambique Channel, partly due to local funneling of winds in the area, and as stronger fronts pass. The faster north to south currents also aid in bringing larger post-frontal passage S-SW seas, with such seas reaching as high as 10-12 feet as S'ly sets run against the faster currents across the area. On the subject of currents, outside of Mozambique Channel, currents across the area generally run from east to west, and northeast to southwest on the north and northwest sides of the South Equatorial Current. By and large, slower currents are found, averaging anywhere from 0.4-0.7 knots outside of the faster current areas mentioned previously. SOUTH OF MADAGASCAR/MOZAMBIQUE CHANNEL TO SOUTH AFRICA: We're looking farther south, and as the more seasoned veterans of the sea can attest to, we're looking at an area that is not without its weather dangers and bouts of adverse conditions. The worst of the conditions occurs during the winter season, as stronger gales/storms pass off to the south, and their associated strong cold fronts approach and pass from the west. With the approach of fronts, winds veer, becoming north to northwest to west, increasing and often approaching gale force. With the passage of fronts, winds shift, becoming S-SW, and periods of gale to storm force winds often occur, especially along and near the southern African coast. These winds often last about 24-36 hours before high pressure moves in from the west and winds ease. Post-frontal passage seas are typically from the south, southwest, and west, and can be quite large, often reaching as high as 12-15 feet. 10-15 feet, are common during these times, especially farther south, in and near Mozambique Channel. These larger seas are found farther to the north and east as well, though farther north, the seas will tend to be longer-period and somewhat lower than those farther south. As transitory ridges move farther east and merging of highs occurs, winds veer, becoming E-SE. Easing of winds and abatement of combined seas occurs farther south, in and near Mozambique Channel, as veering occurs, and as fetch becomes more limited. Further easing in winds occurs throughout the area as winds veer further, becoming northerly and easterly in direction as the next cold front approaches from the west (Figure 2). During the remainder of the year (September through October), the weather is certainly active, though cold fronts tend to be somewhat weaker and less frequent than during winter. Generally speaking, one can expect a frontal passage to occur about every three to four days, with fronts extending as far north as 25S-30S, moving well into the southwest Indian Ocean before encountering ridging from high pressure farther east and slowing/weakening later on. As for our semi-permanent high pressure ridge, that particular feature is still prevalent, and during this period generally extends as far north as 15S. As with winter months, the ridge will be reinforced and intensify some as transitory high pressure again the faster north to south currents in and near Mozambique Channel can induce even larger sets, often well in excess of 10 feet when stronger fronts and following transitory highs move in/south of the area. Any southeast to southerly seas, however, will tend to be longer- period the farther north one travels. Again, breaks in E-SE trade winds will occur as fronts pass off to the south. These breaks will normally last one to two days at a time, and will occur in the form of lighter N-NE-E winds, generally from force 3-5. Combined seas in turn will abate and become longer-period, generally easterly in direction, generally from 4-7 feet. Now we move onward through winter (June through August), and the weather during this time can be summed up in one word: active. Cold fronts are more frequent and stronger during this time, often extending as far north as 25S. Ridging from high pressure tends to be weaker and somewhat farther east as well, allowing fronts to maintain their strength longer as they move toward/through the southern portion of the region, although portions of persistent ridging in the South Atlantic will break away and move into the Indian Ocean in the wake of fronts, eventually merging with the Indian Ocean ridge. The passage of fronts and approach of following high pressure ridges west of fronts will often bring surges of higher SE-S winds. Gale force winds and large SE-S seas, often as high as Figure 2 -- Typical winter patterns across the Southwest Indian Ocean, including stronger, more frequent cold fronts and passage of transitory highs (symbolized with blue H's).
2008 - 2009
2013 - 2014