Isaac (2012)

A tropical wave that moved off Africa on 16 August organized into a tropical depression on 21 August about 625 nautical miles east of the Lesser Antilles. It became Tropical Storm Isaac later that day and tracked generally westward across the Lesser Antilles and the eastern Caribbean, moving over southern Haiti and southeastern Cuba on 25 August. Isaac then moved northwest through the Straits of Florida, entered the southeastern Gulf of Mexico on 27 August, slowly strengthened, and slowed as it neared the U.S. Gulf Coast before making final landfalls in Louisiana. The system weakened over land and became a remnant low over Missouri on 1 September.

Isaac made several landfalls: near Jacmel, Haiti about 0600 UTC 25 August as a tropical storm with estimated winds of about 55 kt (about 63 mph); near Cajobabo (Guantánamo), Cuba around 1500 UTC 25 August with about 50 kt (about 58 mph); at Southwest Pass at the mouth of the Mississippi River about 0000 UTC 29 August as a Category 1 hurricane with peak winds near 70 kt (80 mph); and again near Port Fourchon, Louisiana about 0800 UTC 29 August with similar intensity.

The storm’s maximum analyzed intensity was 70 kt (80 mph) with a minimum central pressure of 965 mb, making Isaac a Category 1 hurricane at peak. That peak occurred between about 28 August 1800 UTC and 29 August 0600 UTC before it weakened over land.

Isaac produced large storm surge and heavy rainfall. The highest tide-based surge recorded by a NOAA gauge was 11.03 ft above normal at Shell Beach, Louisiana. Other measured surges included 6.69 ft at Pilottown (near the Mississippi River mouth), 6.35 ft at New Canal Station in New Orleans, and 8.00 ft at Bay Waveland Yacht Club, Mississippi. Inundation estimates above ground level reached roughly 10–17 ft in parts of Plaquemines Parish, 8–12 ft in St. Bernard Parish, and 4–8 ft in parts of Orleans and St. Tammany Parishes. Rainfall maxima included 22.20 inches in Pascagoula, Mississippi; 20.66 inches in New Orleans, Louisiana; 16.18 inches in Barahona, Dominican Republic; and locally up to about 15.9 inches in western Palm Beach County, Florida (Lion Country Safari area). Puerto Rico totals reached about 9.28 inches north of Ponce; eastern Cuba reported up to 14.08 inches.

Isaac was directly responsible for an estimated 34 deaths: 24 in Haiti, 5 in the Dominican Republic, and 5 in the United States. In the U.S. the fatalities included storm-surge drownings in Braithwaite, Louisiana, and wind-related deaths from trees falling on vehicles. Extensive impacts occurred in southeastern Louisiana where surge flooded areas outside the federal levee system, damaging tens of thousands of homes (Louisiana estimated about 59,000 homes damaged). Insured losses in the U.S. were estimated around $970 million, with total U.S. damages (including uninsured losses) near $2.35 billion. Significant crop losses (notably sugarcane) and widespread power outages also occurred.

Noteworthy details: Isaac was a very large storm with a broad wind field, which produced prolonged surge and flooding along the northern Gulf Coast. The U.S. Army Corps of Engineers’ post-Katrina federal surge protection around New Orleans generally held, protecting much of the metro area, while unprotected and non-federal levees were overtopped in places (notably Plaquemines Parish). Forecasts of Isaac’s track were generally accurate and better than climatology and most guidance, though 3–5 day forecasts initially biased landfall too far east. The storm produced about 17 tornadoes in the U.S., mostly weak but including one EF‑2, and later spawned additional tornadoes from its remnants over the Midwest.