The Great Southern Route : 2013 - 2014
GSR|65 October, when trade wind surges are most common. Combined seas will generally be E-SE in direction, no more than 7-8 feet, and will tend to be lower and longer-period, consisting mainly of E-SE swells the further north one travels, where lighter winds are more common. Breaks in the E-SE trade wind regime will occur when slowing/stalling and weakening frontal systems yield more N-NE-E winds. This is most likely to occur near and west of 160W and during the period from May through September, when cold fronts in the Southwest Pacific tend to advance further east before any stalling/ weakening occurs. N-NE-E winds are generally from force 3-5, with E-SE combined seas lowering and becoming long-period, mixing with N-NE-E sets of no more than 5-6 feet. The Eastern and Central Pacific: 10S to 30S and East of the International Dateline To South America: Again, high pressure is dominant, especially across eastern waters and during the period from November through April, when cold fronts are less prevalent. This means more E-SE trade winds, which will tend to be stronger, reaching gale to near gale force, during wind surges that occur when merging of high pressure ridges occurs. E-SE combined seas tend to prevail as well, longer-period as one travels further north, closer to 10S where higher wind surges are less severe (typically no more than force 6). Sea heights will generally range from 5-9 feet across the area. However, during wind surges, larger sets, as much as 3-5 feet higher can occur, especially across more southern waters (south of 15S-20S), where wind surges are more severe and there is more of a shorter, wind-driven component to the seas. Breaks in the E-SE wind regime will occur as cold fronts move into the region. This is most likely to occur in waters west of 140W during the period from May through September, with fronts eventually slowing, stalling, and weakening near/west of 140W. In this region, cold fronts and resultant weakening of high pressure farther east will induce a veering of winds to more of a NW-N-NE direction, speeds generally from force 3-5, with combined seas lowering and becoming longer-period, generally no more than 6 feet. The tropical season for this region occurs primarily during the period from November into April, and only in the extreme western portions. The peak months for concern are January/ February, as ocean waters are warmest during this period. During May through October, tropical concerns are just about non-existent due to cool ocean water and stronger winds aloft. In this region, typical tropical cyclones develop in the Solomon Islands to north of Fiji, and typically track southeast or south-southeastward to the dateline or 175W. After crossing the dateline, systems typically weaken rapidly due to cooler water further south. Tropical systems rarely form east of the dateline, and never near South America, although, El Nino regimes, particularly stronger El Ninos that are associated with well- above normal sea surface temperatures can allow for cyclone development well east of the dateline, as far east as 150W (certainly a rarity under "normal" circumstances). Once formation occurs, these "rare" tropical cyclones will tend to track in a general W-SW-S'ward motion, weakening as they get further south (south of 25S, in cooler wind surges in the Southern Hemisphere will at times bring larger, long-period E-SE-S swells, generally as high as 7-8 feet. This is most likely to occur during the period from mid to late spring (May/June) through early to mid-Autumn (late October/November), when high pressure in the Southern Hemisphere tends to be larger and stronger than during other times of the year. For most of the year, a countercurrent is centered about 150 nautical miles south of the Gulf of Panama. Closer to the Colombian coast, the current flows northward. This is part of the cool Humboldt Current, which feeds into the east to west moving South Equatorial Current farther west. Along 81W, the current flows southward, and is weakest during the winter months. Otherwise, from this countercurrent southwest to the Galapagos, a W-NW flowing current is typical, varying little throughout the year. These currents usually provide a favorable boost for transits from Panama to the Galapagos, with only a small negative impact for northbound transits. Equatorial Pacific (Equator to 10S, East of 170E): It's pretty much trade winds all the way here. That's the dominant wind regime in place across this part of the world. More specifically, we're talking about E-SE winds, as the aforementioned broad equatorial low pressure trough interacts with a rather persistent high pressure ridge farther south. Over the course of the year, we will see an overall northward/southward "oscillation" in the positioning of both the trough and ridge, farther south during much of the latter half of the year (late July/August through December), with a northward progression during much of the first half of the year. E-SE winds will generally tend to be higher the farther south one travels, further away from the axis of the equatorial trough. Generally speaking, wind speeds will not exceed force 4-5, though merging of high pressure ridges will bring general 1-3 day periods of winds as high as force 6, particularly during the period from May through winds are less likely to occur, and are mainly due to a westward building of a semi-permanent high pressure ridge, building into the western Caribbean from the north and east. Looking farther south toward the Galapagos, the main weather feature in place is a broad, elongated trough of low pressure, oriented east to west across the equatorial Pacific. It is on the northern extent of this trough that we find the so- called "Inter-tropical Convergence Zone" (ITCZ), where N-NE-E winds further north "converge" with SE-S-SW winds further south, and where clusters of showers and squalls develop and move in a general westward motion across the Eastern Pacific. During the summer months, the ITCZ is about as far north as one might expect at any point in the year, generally found about as far north as 12N-15N. As time goes on, the ITCZ progresses farther south, and by December/January, it reaches its southernmost point, generally between 02N and 05N. Squalls within the ITCZ are generally disorganized, especially later in the year when the ITCZ is situated farther south, bringing only periodic and localized areas of higher winds and seas, along with reduced visibility. However, as we get into Tropical Season in the Eastern Pacific, more persistent squall areas can and do become tropical cyclones, primarily in waters farther west, west of the Gulf of Panama. Once south of the Gulf of Panama, the weather to the Galapagos tends to be (for the most part) rather benign. General wind directions are E-SE- SW and for the most part, light, no more than force 3-4. Of course, squalls within the ITCZ will bring higher winds and seas and periods of reduced visibility (below 2 nautical miles in heavy/severe squalls), but these bouts of adverse weather tend to be rather localized, confined to areas in or near squalls themselves. Combined seas will generally vary from E-SE- SW, no more than 5-6 feet south of the Gulf of Panama. However, stronger and prolonged trade Figure 5: Typical annual weather pattern from Panama to the Galapagos.
2010 - 2011