The Great Southern Route : 2010 - 2011
GSR | 069 Speaking of the semi-permanent ridge, it is still a dominant feature this time of year, though at a somewhat weakened state, as compared to winter months. The axis of the ridge during the period is generally found between 32S and 35S, with ridging as far north as 15S-20S. Periodic weakening of the ridge will occur as fronts move into the Indian Ocean, though the ridge later becomes "reinforced" and builds farther north/ west as transitory highs/ridges from the South Atlantic move in and merge with this ridge. Again, east to southeast trade winds are most commonly found, speeds generally from force 4-6. However, surges of higher SE winds, generally as high as force 6-7 are found farther south (south of 15S), as ridging from high pressure intensifies. This is also common in southeast to south winds, especially in Mozambique Channel, where local "channeling" or funneling" of winds exists, after fronts pass near/south of the region. Weakening of the ridge ahead of fronts will induce a veering of winds, generally N-NE-E in direction, with speeds generally from force 3-5. Combined seas will tend to be from the east to southeast, heights generally from 4-8 feet, though note that the passage of cold fronts and resultant higher wind surges can in fact bring more SE-S seas. These can often reach as high as 8-10 feet, especially toward late April/May, when fronts tend stronger. In fact, southerly seas weakening fronts farther west (See Figure 1). East to southeast winds are most commonly found during summer, with speeds generally from force 4-6, and E-SE combined seas averaging from 4-7 feet. Higher winds (more like force 5-6) are found where there is greater interaction between persistent ridging (high pressure) across the area, and the Equatorial Trough to the north. This will generally be confined to waters south of 10S-15S. Breaks in the E-SE trade wind regime develop when ridging weakens, normally occurs as cold fronts move into the southwest Indian Ocean and weaken. As this occurs, winds veer some, becoming NE-E, with speeds generally from force 3-5, and longer- period Easterly combined seas generally from 4-7 feet. Note that protected areas (in immediate coastal waters of western Madagascar for example) tend to see somewhat lower seas (more toward the lower end of the combined sea ranges), as "fetch" becomes more limited. Later in the year (March through May), we talk less about the tropics to be sure, as cyclone frequency decreases. In fact, by late April/May, we are hardly talking about the tropics at all, but cold fronts do begin to enter the weather picture. Fronts extend farther north than their summertime counterparts, and by May are found as far north as 30S, "emerging" into the southwest Indian Ocean about every three to four days, and weakening as they encounter the persistent semi-permanent ridge off to the east. return flow from the North Equatorial Current, found just off to the north in the northern Indian Ocean. Speeds within the Equatorial Current average close to 1.0 knots, though faster speeds are often noted, especially during the summer season, when speeds run from 1.0-1.5 knots. THE SOUTHWEST INDIAN OCEAN -- SEYCHELLES TO MAURITIUS/LA REUNION AND MADAGASCAR/MOZAMBIQUE CHANNEL: This area is not without its dangers, and we have a little more to talk about in this region. The weather tends to be more volatile than areas farther north, and the effects from tropical cyclones and (to a somewhat lesser extent) cold fronts are always to be considered when traveling in this part of the world. Paramount in importance is the tropics. Tropical cyclone frequency increases during the late spring and early summer (November/December and much of January), reaching its "peak period during late January and February. Cyclones will normally begin their life cycle as disorganized or poorly organized squall clusters on the south side of the Equatorial Trough mentioned previously, and are generally found in the Indian Ocean waters between 08S and 15S during their formative stages of development. With time, these squalls will initially track southwest to westward, and in many cases become better organized, developing into full fledged tropical cyclones. As they encounter a "weakness" in the ridging to the south, tropical cyclones will tend to turn south to southwestward, and eventually, they will weaken and become non-tropical entities as they encounter the cooler waters and more hostile environment aloft south of 25S. Given the typical south to southwest turn of tropical systems, one must always be mindful of the possible requirement of evasive action to avoid any potential impacts from such systems. Fortunately, in our advanced satellite age, and with the wealth of real-time data that we Meteorologists have at our disposal, these systems almost never come without warning, and with proper planning and guidance, the chances of any direct impacts is slim to none. Aside from the tropics, trade winds dominate dAring the summer season. Cold fronts remain well to the south (generally south of 35S) and weaken readily as they move into the extreme southwest Indian Ocean. Persistent high pressure covers much of the Indian Ocean along and south of 15S during December/January, and is about as large and strong as one might expect at any point in the year, showing only the slightest and most subtle changes in coverage and strength, governed mainly by the location of the Equatorial trough and the approach of any Figure 1 -- Typical summer weather patterns across the Southwest Indian Oceans. The directions of tropical cyclones are denoted by the arrows pointing west to southwestward.
2008 - 2009
2013 - 2014