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At 13/03Z NHC upgraded TD12 to Tropical Storm Julia - the tenth named storm of the season. Julia was located about 110 miles to the southeast of the southern Cape Verde Islands and with movement to the west northwest becoming more northwest at 10mph, a Tropical Storm Warning has been issued for those southern islands. Julia is expected to become a Hurricane on Tuesday. Wih some factors favoring an increase in intensity and increasing windshear and cooler SSTs in a couple of days favoring a decrease in intensity, the intensity forecast beyond Tuesday could see some fluctuations.
Igor is...well, simply an amazing storm with sustained Cat IV winds now at 130 knots and the possibility of 140 knots (Cat V) by 12Z on Monday. Although some erosion has been noted on the southeast core, this could simply be associated with the directional change of the past few hours to slightly south of due west, and there is a pocket of drier air ahead of the system for the next couple of days but its not that significant. Near-term motion to the west and west northwest is anticipated, however, the long term is still a bit uncertain with a few models hinting at a turn back toward the west northwest, i.e., the weakness in the ridge does not fully capture the system. However, at the moment this is still an outlier scenario - but folks in the northern Leeward Islands should closely monitor Igor and wait for the expected turn to the northwest.
Veering wind- A wind that shifts in a clockwise direction with height. For example, a south wind at 850 mb and a west wind at 700 mb would be a veering wind. Also can be a wind shift at the surface or a particular pressure level in which over time the wind shifts in a clockwise direction at a point location.
Wind is the movement of air. To move the air a force is required. The initiating factor that develops wind is due to horizontal temperatures differences in the troposphere. Air masses (and air with different temperature and moisture properties on smaller scales) will have different densities and these density differences cause pressure differences between the regions the air masses or smaller scale air regions meet. The force responsible for moving the air is the Pressure Gradient Force. There are other factors that influence the wind speed and direction (Coriolis, friction, centrifugal, etc.) but the Pressure Gradient Force starts it off. Since temperature differences occur on all scales (global, synoptic, mesoscale, and smaller), wind patterns are also on all of these scales.
Rainfall depends on topography, ranging from less than 600 mm along leeward coasts in rain-shadow to over 5000 mm on windward slopes of mountains. Most inland areas have annual rainfall within the 1500-2000 mm per annum range. All climates in the region are seasonal with, at sea-level in most years, at least one dry month when rainfall is less than 100 mm. The main dry period is usually between January and April;
there may be a second dry period in more southerly latitudes in July to September.
As two impressive hurricanes continue spinning far out to sea, a bit of a sneaker of a system which we have been following (Invest 92L) is now developing impressively in the favorable environment of the west-central Caribbean, and if current trends continue, advisories could very easily and quickly be issued for west Caribbean nations and/or their nearby islands later today or tonight. Interests in and around the western Caribbean, including the Yucatan peninsula, may want to start taking some tentative precautions for very heavy rain and stout wind, regardless.
Recon is currently back en route to Invest 92L.
Two tropical cyclones approaching each other may or may not collide, as shown in the diagram in Figure 1. The letter A designates the initial positions of two storms. As they come nearer, the circulation of each storm influences the track of the other, and the track of each becomes an arc about a central point labeled M. The motion depicted here is relative to M, but bear in mind that M is moving with respect to the Earth's surface. At some later time, the cyclones reach point C, when they begin to orbit about each other. Mutual orbiting is in progress at point O. If the two storms are similar in size, they continue in orbit and eventually escape each other (E). If one is considerably larger and more intense than the other, the two storms can merge, the larger one engulfing the smaller one. Merging does not imply strengthening. The opposite is more likely because the flow at the edge of one storm opposes the flow at the adjacent edge of the other. In 1995, Hurricane Iris merged with much weaker Tropical Storm Karen and absorbed it.