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By: KoritheMan , 4:13 AM GMT on November 27, 2012
Tropical Cyclone Report
Ernesto moved uneventfully through the Caribbean Sea as a tropical storm before becoming a hurricane as it approached the Yucatan Peninsula. Ernesto then made a second landfall over extreme southeast Mexico as a tropical storm. Ernesto's remnants contributed to the formation of Tropical Storm Hector in the Eastern North Pacific.
a. Storm History
Ernesto's development began when a vigorous tropical wave emerged from the coast of Africa on 23 July. While in situ observations are relatively scarce in this area of the Atlantic, ASCAT ambiguities suggest that the wave was of fairly high amplitude, and it contained a vigorous lower- to middle tropospheric cyclonic circulation envelope which appeared to be closed at times. Notwithstanding, there was little overall development for the next several days as the wave marched westward, possibly in response to a large dust-laden airmass associated with the Saharan Air Layer (SAL) that prevailed over much of the tropical Atlantic during this time. Possibly enhanced by the Intertropical Convergence Zone (ITCZ), the wave began showing signs of organization on 28 July, when a broad low pressure area is estimated to have developed along the wave axis. Microwave data (not shown) showed the inner structure beginning to look less skeletal around midday 30 July, which was concurrent with satellite images showing developing banding features.
Subsequently, the tropical wave began to increase in forward speed while gradually turning toward the west-northwest. Development continued, and it is estimated that the system became a tropical depression near 1800 UTC 1 August while centered approximately 700 miles east-southeast of Barbados. The “best track”chart of the tropical cyclone’s path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 1. The depression failed to strengthen initially, and the cloud pattern as a whole was disorganized. Based on a flight from a reconnaissance aircraft and a slightly improved convective presentation in satellite images, the cyclone is assumed to have become a tropical storm around 0000 UTC that day. Ernesto appears to have strengthened a little as it moved through the eastern Caribbean on 4 August, but the low-level center remained displaced to the west of the convection due to westerly speed shear caused by the fast forward motion of the tropical storm as it was steered to the north of a strong subtropical ridge. The cyclone started to lose organization again late that same day, and there is some doubt as to the veracity of a closed circulation during that time.
Little change in strength was noted over the next couple of days as Ernesto continued westward. As the system approached the western Caribbean late on 6 August, however, it began to strengthen, possibly in response to a relative decrease in the forward speed in response to an upper-level trough that was moving into the southern United States. Based on satellite pictures and data from a reconnaissance aircraft, it is estimated that Ernesto became a hurricane just before 1800 UTC 7 August, centered about 250 miles east-northeast of Belize City. Ernesto continued to strengthen up until landfall, reaching its maximum estimated intensity of 75 kt near 0000 UTC 8 August while located about 60 miles east of Chetumal, Mexico. The hurricane made landfall along the southern coast of the Yucatan in a remote area just south of Chetumal just after 0200 UTC at peak intensity. At that time, satellite and aircraft data indicated that Ernesto was strengthening, and could have been going through a rapid deepening phase. The eye briefly became better defined after landfall near 0600 UTC, but the inner core quickly collapsed as the cyclone continued inland. Ernesto weakened below hurricane status near 1200 UTC that day while moving overland.
The cyclone entered the Bay of Campeche a little after 1800 UTC 8 August and began to gradually turn southwestward under a building low- to mid-level ridge over the Gulf of Mexico. Despite the weakening while over Yucatan, Ernesto's cloud pattern remained well-organized. Based on surface observations and satellite data, Ernesto made a second landfall along the coast of Mexico along the southeast portion of the coast near Coatzacoalcos near 1530 UTC 9 August as a 50-kt tropical storm. The tropical cyclone weakened after landfall, and is estimated to have dissipated over the Sierra Madre Oriental near 0600 UTC 10 August. The remnants -- apparently a mid-level circulation -- continued moving southwestward, where they entered the Eastern North Pacific and contributed to the formation of a large area of disturbed weather which ultimately spawned Tropical Storm Hector.
b. Meteorological Statistics
Observations in Ernesto include the satellite-based Dvorak intensity technique, although to a lesser extent since reconnaissance observations in the storm were widespread. Various microwave data were used to track the tropical cyclone as well, most notably the SSMI/S unit.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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