Meteorological history of Hurricane Ivan
The meteorological history of Hurricane Ivan, the longest-lasting tropical cyclone of the 2004 Atlantic hurricane season, lasted from late August through late September. Ivan was the southernmost major hurricane on record.[1]
Formation and intensification
On August 31, a large tropical wave moved off the west coast of Africa. A tropical system along the wave axis contained a low pressure area as well as an impressive outflow pattern, though initially its convection was disorganized and limited.[1] By September 1 a 690 mile (1115 km) was evident on satellite imagery, well to the southeast of the Cape Verde Islands,[2] and several hurricane forecast models anticipated development and strengthening.[3] As it tracked quickly westward, the convection organized and developed into rainbands – bands of showers and thunderstorms that spiral cyclonically toward the storm center – and late on September 1 meteorologists began tracking the system using the Dvorak technique. Low amounts of wind shear and favorable outflow allowed vigorous deep convection to develop and persist near the center, and by 1800 UTC on September 2 the system developed into Tropical Depression Nine about 450 miles (730 km) southwest of Praia, Cape Verde.[1]
Upon being classified as a tropical cyclone, the depression was embedded within a deep easterly steering current provided by a ridge to its north. Expected to track across sea surface temperatures greater than 82 °F (28 °C), the cyclone was forecasted to gradually strengthen and within four days attain hurricane status;[4] the Geophysical Fluid Dynamics Laboratory predicted the depression to reach Category 4 status on the Saffir-Simpson Hurricane Scale within three days. Increased northeasterly wind shear shifted the center to the northeastern edge of the deep convection,[5] and despite the shear and its relatively low latitude of 9.7° N, the depression strengthened to attain tropical storm status early on September 3; upon reaching the intensity, the National Hurricane Center classified the system as Tropical Storm Ivan.[1]
Tropical Storm Ivan gradually became better organized as wind shear decreased, and its outflow expanded in all quadrants. Satellite imagery late on September 3 depicted a well-defined curved band wrapping around much of the circulation.[6] The next day, the deep convection temporarily became ill-defined,[7] before reorganizing and developing an eye feature.[8] Convection strengthened further as the feature transitioned into an eye,[9] and Ivan became a hurricane at around 0600 UTC on September 5. After reaching hurricane status, Ivan began to rapidly intensify with continued favorable conditions, and in an 18 hour period the pressure dropped 39 mbar (hPa) as the winds increased by 60 mph (95 km/h); early on September 6 Ivan attained an initial peak intensity of 135 mph (215 km/h) while located about 825 miles (1330 km) east of the island of Tobago in the southern Lesser Antilles.[1]
Reaching Category 4 status on the Saffir-Simpson Hurricane Scale at 10.6° N, Ivan became the southernmost major hurricane on record;[1] at the intensity, the hurricane maintained very strong convection in its core with a well-defined eye. Operationally, the probability for further rapid strengthening was nearly nine times the average of a typical hurricane. Accordingly, Ivan was forecasted to pass near Barbados with winds of about 150 mph (240 km/h).[10] Shortly after attaining Category 4 status, the outer convection of the hurricane became ragged.[11] Hurricane Hunters found a Saharan Air Layer in the northern portion of the eye,[12] leaving the eyewall eroded which caused a marked decrease in winds;[13] by late on September 6 Ivan weakened to winds of 105 mph (165 km/h).[1] The inner eyewall dissipated as a 23 mile (37 km) outer eyewall became dominant, and concurrently the overall organization of the hurricane improved.[14] Ivan again attained major hurricane status as it approached the Lesser Antilles, and at 2130 UTC on September 7 the cyclone passed 7 miles (11 km) south-southwest of the southern tip of Grenada, its closest approach to the island.[1]
Caribbean Sea
Gulf of Mexico and Alabama landfall
Redevelopment and demise
See also
References
- ^ a b c d e f g h Stacy Stewart (2004). "Hurricane Ivan Tropical Cyclone Report". National Hurricane Center. Retrieved 2007-10-19.
- ^ Nelson (2004). "September 1 Tropical Weather Discussion". National Hurricane Center. Retrieved 2007-10-19.
- ^ Berg (2004). "September 1 Tropical Weather Discussion (2)". National Hurricane Center. Retrieved 2007-10-19.
- ^ Knabb and Pasch (2004). "Tropical Depression Nine Discussion One". National Hurricane Center. Retrieved 2007-10-19.
- ^ Franklin (2004). "Tropical Depression Nine Discussion Two". National Hurricane Center. Retrieved 2007-10-19.
- ^ Knabb and Pasch (2004). "Tropical Storm Ivan Discussion Five". National Hurricane Center. Retrieved 2007-10-19.
- ^ Pasch (2004). "Tropical Storm Ivan Discussion Eight". National Hurricane Center. Retrieved 2007-10-19.
- ^ Beven (2004). "Tropical Storm Ivan Discussion Ten". National Hurricane Center. Retrieved 2007-10-19.
- ^ Beven (2004). "Hurricane Ivan Discussion Ten". National Hurricane Center. Retrieved 2007-10-19.
- ^ Jarvinen and Hennon (2004). "Hurricane Ivan Discussion Fifteen". National Hurricane Center. Retrieved 2007-10-19.
- ^ Pasch (2004). "Hurricane Ivan Discussion Seventeen". National Hurricane Center. Retrieved 2007-10-19.
- ^ Lawrence and Hennon (2004). "Hurricane Ivan Discussion Nineteen". National Hurricane Center. Retrieved 2007-10-19.
- ^ Pasch (2004). "Hurricane Ivan Discussion Eighteen". National Hurricane Center. Retrieved 2007-10-19.
- ^ Stewart (2004). "Hurricane Ivan Discussion Twenty". National Hurricane Center. Retrieved 2007-10-19.