This interaction with land disrupted Irma’s structure a bit, as a hurricane requires plenty of deep warm water beneath the storm’s center to maintain the extremely low pressure and strong winds. Irma moved west along or just inland from the northern coast of Cuba on September 9 th. Irma intensified to a category-5 level once again that evening, with top winds of 160 MPH, as it approached the northern coast of Cuba. The storm finally “weakened” to a category-4 hurricane on September 8 th, but still had devastating winds of 155 MPH while moving through the southern Bahamas. 5 NASA’s landsat-8 satellite images, before & after Irma. The islands, which used to appear green to the special satellite sensor due to their dense coverage of plants and trees, are now brown.įig. 5 shows the massive defoliation across some of the Virgin Islands which were struck by Irma at peak intensity. While it will take time to realize all of the impacts from Irma, some were immediately apparent, even from space. 4 Satellite montage of Irma using GOES IR images and NHC advisories. Irma was a category-5 hurricane for 3 days (Fig. While category-5 hurricanes are rare, it is even more rare for such storms to maintain this status for such a long period of time. Over the next few days Irma continued moving west, passing through the northeast Leeward Islands, Virgin Islands, and just north of the islands of Puerto Rico and Hispaniola, while maintaining its category-5 winds. This made Irma the strongest hurricane ever observed in the open Atlantic Ocean, and one of only 5 hurricanes with measured winds of 185 MPH or higher in the entire Atlantic basin. The storm became a rare category-5 hurricane on September 5 th, with maximum sustained winds of 185 MPH. Image courtesy of UW CIMSS.Īs Irma began to approach the northern Leeward Islands on September 4 th and 5 th, the hurricane rapidly intensified while moving over warmer water and into a more moist atmosphere. Irma’s intensity remained fairly steady for the next few days while moving into a region with drier air aloft (Fig. Such rapid strengthening is unusual for storms in the far eastern Atlantic. Over the following 30 hours Irma intensified into a major hurricane with highest sustained winds of 115 MPH, a category-3 storm on the Saffir-Simpson Hurricane Wind Scale. Tropical Storm Irma formed in the far eastern Atlantic Ocean, just west of the Cape Verde Islands, on the morning of August 30 th. light wind shear). Hurricane Irma shown using red hurricane symbol. Image is vertical wind shear in knots, with black and dark blue being most favorable for tropical cyclone intensification (i.e. 2Upper-level flow (white lines with arrows), based on satellite estimates of 200 mb winds (40,000 ft AGL). 1National Hurricane Center’s 5-day forecast probability for a tropical disturbance emerging off the west African coast on August 27th. Sea surface temperatures were above average (generally in the lower to mid 80s F across the tropical Atlantic), and there was an area of light winds in the upper atmosphere, which allowed the developing storm circulation to grow vertically deep (Fig. In late August and early September, however, the atmospheric and oceanic conditions in the tropical Atlantic were favorable for tropical cyclone development. This can be due to a number of factors, including blasts of dry, stable air from the Saharan desert, strong upper-level westerly winds, or a lack of the necessary atmospheric “spin” needed to generate a counterclockwise circulation. Such disturbances move off the African coast every few days during August and September, however, most of them fail to develop into tropical cyclones. Like many of the most notorious Atlantic hurricanes, Irma began as a weak wave of low pressure accompanied by disorganized showers and thunderstorms which emerged off the west African coast on August 27 th, near the peak of the Atlantic hurricane season (Fig. Hurricane Irma was a classic Cape Verde hurricane that will long be remembered for its severity and wide-ranging impacts to several islands in the Caribbean Sea and Florida.
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