Sunday, September 12, 2004


IVAN SEEMS TO SAY "GO WEST"... COULD MEAN HARD GOING IN THE BIG EASY

If you've been following hurricane developments this weekend, then you know that the 'cone of uncertainty' for Ivan's landfall has been drifting slowly westward since Friday. Now New Orleans is just outside the far western edge of the cone, and Tampa in the far eastern side.

If you haven't followed the hurricane as closely, that's okay. It just means you've been able to get out more and enjoy life, whereas unusual types like myself have a tendency to check every sniffle and sneeze of these storms at three hour intervals in between playing with my baby girl.

The 5pm and 8pm advisory indicated winds have leveled out at approx. 150 mph, and pressure has dropped to 915 millibars. The hurricane is continuing a mostly west-northwest motion, and has shown no signs of a turn to the northwest. This is significant for two reasons:

1. The inner eyewall is undergoing a replacement cycle, which means when the intense rainfall and towering thunderstorms in that eyewall spin themselves out, moisture spiraling in from outside the eyewall begins to regenerate the eyewall. If sea surface, pressure and atmospheric conditions are MORE favorable before and during the concentric eyewall replacement cycle, then we usually see a drop in pressure and an increase in wind speed as reported by the reconnaissance aircraft. You also see evidence of this when the colorized banding on the infra-red satellite imagery show the darker reds and purples completing a sphere around the eye.

2. The storm has access to 30c (86 F or higher) surface waters, and steering currents that would have turned it northwest are weaker than anticipated. This spells very bad news for anyone living along the northern Gulf coast from Panama City westward to New Orleans. I It should not be a surprise if the storm regains Category 5 status within 24 hours, perhaps even overnight.

WHAT IS THE BOTTOM LINE IN TERMS OF THE HIGH RISK AREA?

If Ivan the monster misses Cuba, travels through the Yucatan channel, and takes a more gradual turn to the north, New Orleans and the Mississippi Sound may well be in the target zone for landfall. A further shift to the west of the "uncertainty" cone to fully encompass eastern Louisiana, with the Appalachee Bay on the very eastern fringe of the cone will be the reality check for city managers of New Orleans.

IS THERE ANYTHING TO WEAKEN THIS STORM SINCE IT MISSED LAND?

Another weather blog, Fresh Bilge, has discussed the possibility of dry air filtering into the storm from the north. This is a very plausible notion, as there is a broad area of high pressure moving south from the Plains. The high will serve as a blocking feature, protecting the western gulf, as indicated by Accuweather.

Sea surface temperatures in the northeastern Gulf are slightly below average as indicated by this current map maintained by the U.S. Navy. So there are several factors at work which may serve to challenge the storm's ability to remain intense as it travels north. The NHC is fully expecting a northward weakening trend, and reflecting this in their wind speed projections as listed on the recent discussions. Accuweather's Joe Bastardi is skeptical of a northward weakening trend, as he thinks the storm will challenge Camille's intensity. So the lines have been drawn, we shall see who gets it right.

If the track begins shifting westward to encompass New Orleans, I will prepare a revised analysis of what surrounding areas can expect over the next few days leading up to landfall. If you reading this site from anywhere inside the New Orleans to Panama City, there is no harm in making basic preparations now.

Obviously many, many people are eventually going to have to deal with this storm, so our thoughts and prayers are with those families whoever and wherever they will be.

A brief early morning update on Monday, followed by a full update after the 5pm advisory.



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