As Tropical Storm Isaac (soon to be Hurricane Isaac) crosses over the Florida Keys, forecasters keep shifting the track to the west putting New Orleans in its cross hairs and wondering whether this storm will approach the potency of Hurricane Katrina. But, while there are some similarities, this storm will probably not cause the damage seen during Katrina. Here's why:
1. Size of the Storm: Both Isaac and Katrina were abnormally large storms in their scope (distance from the center to the furthest area of tropical storm winds). Larger storms can pack a deceptively large punch even if they don't reach major hurricane status, because Hurricane winds and tropical storm winds (and resulting tornadoes and heavy rain) are experienced over a wider area.
But for the same reason, large storms have a harder time strengthening. A variety of factors lead to the strengthening of tropical cyclones. One of the biggest factors is the presence of warm water. When storms approach the Caribbean, warm water is plentiful. As storms head north late in the Hurricane season (either up the Eastern Seaboard or into the Gulf of Mexico), they can still tap into warm water, but the layer of warm water is shallow. When the ocean churns, cold water is brought up from below. A larger storm is more likely to stir up the water ahead of its path before the center of circulation reaches that water. This makes strengthening slightly more difficult.
2. Interaction with relatively warm Gulf of Mexico water: The most obvious similarity between Katrina and Isaac is that they both enter the Gulf of Mexico at a period when the water is a relatively high temperature. Katrina made its way into the center of the gulf along the loop current (a ribbon of warm water that wraps from the Caribbean Sea, around Cuba, through the Florida Straights and up the East Coast - learn more) and "bombed" into a category 5 hurricane when it was able to tap into the balmy water of an eddy (see the LCE Vortex) that forms in the center of the gulf:
This year is a bit different. Unlike 2005, the loop current phenomenon hasn't really taken shape with the same intensity as 2005. In addition, while meteorologists continue to shift Isaac's path to the west, it will likely miss most of the loop current, instead staying closer to the colder waters near the shore (Isaac's probably path is plotted in red):
Still, Gulf Coast residents should prepare themselves for a dangerous weather event. Because Katrina briefly became a category 5 hurricane, many people forget that it actually weakened significantly before reaching shore at category 3. As we found out, a category 3 hurricane as large (in scope) as Katrina can cause catastrophic damage. Isaac seems unlikely to become a major hurricane (category 3 or higher), but if forecasters continue to slow down its approach and shift it west, it will likely reach category 2, with sustained winds of 105mph.