One of the things discussed during last evening’s update was the dry air that was impeding Isaac’s development, and that appears to be continuing this morning. Although an eye can now be seen forming on satellite, the storm overall continues to have a ragged appearance, especially along it’s northern edge:
The convection to the east of the center is trying to close the eyewall off, and it’s difficult to say whether this will happen or whether it will be another failed attempt given the dry air that continues to plague Isaac’s development. This is not to say, however, that there has not been intensification; because, the pressure has in fact dropped to 978 mb, which is typically a category 2 hurricane based on pressure alone. At the very least, I consider this to be a cat 1 currently. Regardless though, the dry air entrainment and the rather large size of the storm, as pointed out by our own Jim Rinaldi at epawa.net, has largely prevented the winds from increasing to correlate with the pressure drop. This scenario is similar to what was seen with Hurricane Irene last year – very low central pressures, which normally would mean a strong hurricane, but a disconnect between the pressure and the surface winds.
Additionally, Isaac has appeared to jogged a bit to the west overnight, and appears, for the time being, to be moving more west-northwest. Hopefully, this trend will continue and prevent the strongest winds (and therefore the largest storm surge) out of the city of New Orleans. A few of the most recent model runs have the center passing fairly far south of the city, including the overnight European, which has the eye a good 50 miles to the south, shown below, courtesy of Weatherbell Analytics, LLC, at weatherbell.com):
The next 12 hours will be critical, as we will see whether (1) the storm continues in a more WNW rather than NW direction, and (2) how much intensification we get as it approaches the coast. Hurricane Charlie remains in the back of my mind, because that storm went from a category 1 to category 4 storm in a matter of hours, so New Orlean’s is not clear of this threat by a long shot. But one thing that is clear – there will be a tremendous amount of rain associated with this storm, which will cause a great deal of flooding on it’s own, especially if the storm slows down as it approaches the coast as modeled.
As usual, we will have updates on our Facebook page as warranted, and at weatherbell.com, which gives you in depth analysis by some of the best in the business, as well as models that are second to none, as a discounted price that is available only on our website, http://www.epawa.net.