Five Years Ago Yesterday, What Became Katrina First Took Shape N. Of Puerto Rico

[hatrack]

EDIT

The complex genesis of Katrina involved the interaction of a tropical wave, the middle tropospheric remnants of Tropical Depression Ten, and an upper tropospheric trough. This trough, located over the western Atlantic and the Bahamas, produced strong westerly shear across Tropical Depression Ten, causing it to degenerate on 14 August approximately 825 n mi east of Barbados. The low-level circulation gradually weakened while continuing westward, and it eventually dissipated on 21 August in the vicinity of Cuba. Meanwhile, a middle tropospheric circulation originating from Tropical Depression Ten lagged behind and passed north of the Leeward Islands on 18-19 August. A tropical wave, which departed the west coast of Africa on 11 August, moved through the Leeward Islands and merged with the middle tropospheric remnants of Tropical Depression Ten on 19 August and produced a large area of showers and thunderstorms north of Puerto Rico. This activity continued to move slowly northwestward, passing north of Hispaniola and then consolidating just east of the Turks and Caicos during the afternoon of 22 August. Dvorak satellite classifications from the Tropical Analysis and Forecast Branch (TAFB) of the Tropical Prediction Center (TPC) began at 1800 UTC that day. The upper tropospheric trough weakened as it moved westward toward Florida, and the shear relaxed enough to allow the system to develop into a tropical depression by 1800 UTC 23 August over the southeastern Bahamas about 175 n mi southeast of Nassau. The depression was designated Tropical Depression Twelve rather than “Ten” because a separate tropical wave appeared to be partially responsible for the cyclogenesis, and, more importantly, the low-level circulation of Tropical Depression Ten was clearly not involved.

The “best track” of the path of the center of Katrina is displayed 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 continued to become organized over the central Bahamas during the evening of 23 August. Deep convection increased overnight in the eastern semicircle of the cyclone and formed a well-defined band that began to wrap around the north side of the circulation center early on the morning of 24 August. Based on aircraft reconnaissance flight-level wind data, the cyclone became Katrina, the 11th tropical storm of the 2005 Atlantic hurricane season, at 1200 UTC 24 August when it was centered over the central Bahamas about 65 n mi east-southeast of Nassau. Initially the storm moved northwestward within a weakness in the lower tropospheric subtropical ridge. However, as the storm developed an inner core and evolved into a deeper cyclone on 24 August, it came under the influence of a strengthening middle to upper tropospheric ridge over the northern Gulf of Mexico and southern United States. This ridge turned Katrina westward on 25 August toward southern Florida. Katrina generated an intense burst of deep convection over the low-level center during the afternoon of 25 August while positioned over the northwestern Bahamas. Further strengthening ensued, and Katrina is estimated to have reached hurricane status near 2100 UTC 25 August, less than two hours before its center made landfall on the southeastern coast of Florida.

The strengthening ridge over the northern Gulf of Mexico and southern United States produced northeasterly middle- to upper-level tropospheric flow that forced Katrina to turn west-southwestward as it neared southern Florida. Katrina made its first landfall in the United States as a Category 1 hurricane on the Saffir-Simpson Hurricane Scale, with maximum sustained winds of 70 knots, near the border of Miami-Dade County and Broward County at approximately 2230 UTC 25 August. While not discernible in conventional satellite imagery, a well-defined eye became evident on the Miami National Weather Service (NWS) WSR-88D Doppler radar just prior to landfall on the southeastern Florida coast. In fact, the eye feature actually became better defined while Katrina moved inland, and it remained intact during its entire track across the peninsula. The convective pattern of Katrina as it crossed southern Florida was rather asymmetric due to northerly wind shear, which placed the strongest winds and heaviest rains south and east of the center in Miami-Dade County. Katrina continued west-southwestward overnight and spent only about six hours over land, mostly over the water-laden Everglades. Surface observations and velocity estimates from the Miami and Key West Doppler radars indicated that Katrina weakened over mainland Monroe County to a tropical storm with maximum sustained winds of 60 knots. The center of Tropical Storm Katrina then emerged into the southeastern Gulf of Mexico at approximately 0500 UTC on 26 August just north of Cape Sable.

Once back over water, Katrina quickly regained hurricane status at 0600 UTC with maximum sustained winds of 65 knots. Even though the center of Katrina continued west-southwestward over the southeastern Gulf of Mexico and away from the southern Florida peninsula, a strong and well-defined rain band impacted large portions of the Florida Keys with tropical storm-force winds for much of the day on 26 August. Sustained hurricane-force winds were briefly measured at Dry Tortugas on the far western end of the island chain that afternoon.

EDIT

http://www.nhc.noaa.gov/2005atlan.shtml

[damntexdem]

1. And a week later was about to hit.

Just as Camp Casey II was breaking up. The double whammy that really hit the Bush Administration.