Hurricane Dean is the fourth named storm, third tropical cyclone, first hurricane and first major hurricane of the 2007 Atlantic hurricane season, the most intense tropical cyclone in the Atlantic Basin since Hurricane Wilma of 2005 and the most intense tropical cyclone to threaten Jamaica since Hurricane Ivan of 2004. A Cape Verde-type hurricane, as of August 19, 2007 it is moving through the eastern portion of the Caribbean Sea west of the Lesser Antilles where it killed 8 people.Storm history
On August 11, 2007, a vigorous tropical wave moved off the west coast of Africa,[1] producing disorganized showers and thunderstorms.[2] It encountered conditions favorable for gradual development,[3] and on August 12 it gained organization and became a low.[4] Strong upper-level easterly winds stalled development by preventing much more organization.[5][6] On August 13 the tropical wave organized and, based on visible and infrared satellite imagery, the National Hurricane Center concluded that it had formed into Tropical Depression Four at 1500 UTC about 520 miles (835 km) west-southwest of Cape Verde.[7]
The depression was already exhibiting persistent deep convection, albeit confined to the western portion of its circulation due to easterly wind shear.[8] The depression was expected to strengthen significantly over the coming days[8] due to abating wind shear and warming sea surface temperatures which created conditions favorable for tropical intensification.[9] The depression moved briskly westward, south of a deep layered ridge,[10] quickly escaping the easterly shear and moving over warmer waters.[11]
Based on microwave satellite images and QuikSCAT data, the depression was upgraded to Tropical Storm Dean at 1500 UTC on August 14.[12] That afternoon its convection waned slightly as part of a diurnal fluctuation, but an AMSU pass suggested growing intensity.[13] Intensity continued to build as convection flared in the center on the night of August 14. This was most likely due to continuing decreases in the easterly wind shear.[14] Dry air and cooler air inflow from the north were slowing structural development, but nevertheless ragged bands began to form on August 15.[15] By mid-morning hints of a banding eye had been spotted on satellite imagery[16] and the storm continued to strengthen.[17] Visible satellite images showed a tightly curved band wrapping around the center later that day and microwave images suggested the formation of a partial eyewall.[18]
Intensification continued through the night[19] and the storm was upgraded to Hurricane Dean at 5 am EDT (9 am UTC) August 16.[20] A strong deep-layered ridge continued to steer the system west, towards the Caribbean Sea.[21] That same afternoon convective banding and increasing upper-level outflow strengthened the storm to a Category 2 hurricane on the Saffir-Simpson Hurricane Scale.[22] The eye disappeared briefly overnight, possibly as part of a diurnal fluctuation,[23] and a ragged eye had returned by the morning of August 17. Dry air intrusion and slight westerly shear appeared to slow but not reverse the storm's development.[24] A reconnaissance aircraft later that day discovered a closed eyewall, and increased banding created a more organized cloud pattern on satellite imagery.[25] Data from the aircraft also indicated that Hurricane Dean had strengthened to a Category 3 hurricane.[26] Satellite imagery on the evening of August 17 showed a well defined eye feature as numerous cyclonically curved convective bands remained over the Lesser Antilles.[27] During the evening of August 17, data from a reconnaissance aircraft showed that Dean had strengthened into a Category 4 hurricane.[28] Additional reconnaissance aircraft equipped with a stepped-frequency microwave radiometer confirmed the Dvorak estimates which showed that Hurricane Dean was steadily intensifying through the night. The aircraft data also showed that the wind radii had increased in all quadrants as the storm grew not only in intensity but also in size.[29][30] Another reconnaissance aircraft on August 18 reported the presence of a double eyewall,[31] indicating an eyewall replacement cycle and causing short term fluctuations in intensity.[32][33] That afternoon the hurricane was seen to have numerous spiral bands and continued to improve its outflow, giving it a well defined satellite presentation.[31] Hurricane Dean weakened very slightly on morning of August 19 and experienced some trochiodal wobbles as it finished the eyewall replacement cycle.[34][35
The depression was already exhibiting persistent deep convection, albeit confined to the western portion of its circulation due to easterly wind shear.[8] The depression was expected to strengthen significantly over the coming days[8] due to abating wind shear and warming sea surface temperatures which created conditions favorable for tropical intensification.[9] The depression moved briskly westward, south of a deep layered ridge,[10] quickly escaping the easterly shear and moving over warmer waters.[11]
Based on microwave satellite images and QuikSCAT data, the depression was upgraded to Tropical Storm Dean at 1500 UTC on August 14.[12] That afternoon its convection waned slightly as part of a diurnal fluctuation, but an AMSU pass suggested growing intensity.[13] Intensity continued to build as convection flared in the center on the night of August 14. This was most likely due to continuing decreases in the easterly wind shear.[14] Dry air and cooler air inflow from the north were slowing structural development, but nevertheless ragged bands began to form on August 15.[15] By mid-morning hints of a banding eye had been spotted on satellite imagery[16] and the storm continued to strengthen.[17] Visible satellite images showed a tightly curved band wrapping around the center later that day and microwave images suggested the formation of a partial eyewall.[18]
Intensification continued through the night[19] and the storm was upgraded to Hurricane Dean at 5 am EDT (9 am UTC) August 16.[20] A strong deep-layered ridge continued to steer the system west, towards the Caribbean Sea.[21] That same afternoon convective banding and increasing upper-level outflow strengthened the storm to a Category 2 hurricane on the Saffir-Simpson Hurricane Scale.[22] The eye disappeared briefly overnight, possibly as part of a diurnal fluctuation,[23] and a ragged eye had returned by the morning of August 17. Dry air intrusion and slight westerly shear appeared to slow but not reverse the storm's development.[24] A reconnaissance aircraft later that day discovered a closed eyewall, and increased banding created a more organized cloud pattern on satellite imagery.[25] Data from the aircraft also indicated that Hurricane Dean had strengthened to a Category 3 hurricane.[26] Satellite imagery on the evening of August 17 showed a well defined eye feature as numerous cyclonically curved convective bands remained over the Lesser Antilles.[27] During the evening of August 17, data from a reconnaissance aircraft showed that Dean had strengthened into a Category 4 hurricane.[28] Additional reconnaissance aircraft equipped with a stepped-frequency microwave radiometer confirmed the Dvorak estimates which showed that Hurricane Dean was steadily intensifying through the night. The aircraft data also showed that the wind radii had increased in all quadrants as the storm grew not only in intensity but also in size.[29][30] Another reconnaissance aircraft on August 18 reported the presence of a double eyewall,[31] indicating an eyewall replacement cycle and causing short term fluctuations in intensity.[32][33] That afternoon the hurricane was seen to have numerous spiral bands and continued to improve its outflow, giving it a well defined satellite presentation.[31] Hurricane Dean weakened very slightly on morning of August 19 and experienced some trochiodal wobbles as it finished the eyewall replacement cycle.[34][35
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