A mid-morning update is due out from the National Hurricane Center (NHC) at 10am CDT. I am not sure whether or not they will "pull the trigger" at that time or wait for the afternoon update (especially since they have been forecasting Isaac to remain a tropical storm until after 2pm today), but based on satellite and radar presentation as well as a few recent ship and aircraft observations, I believe that Isaac has reached hurricane strength. If not, it is extremely close to doing so.
Thunderstorm activity continues to organize around an ever tightening center, as you can see on the above high resolution visible satellite image. You can view a loop of these images (which are being taken once every minute by the GOES-14 weather satellite) by going here. In my opinion this is a sign that Isaac is developing a better defined inner core, which will likely result in rapid intensification over the next 24-36 hours, especially as that core moves out over increasingly warm waters in the Gulf of Mexico.
Computer forecast models continue to come into better agreement that impacts from Isaac will be greatest along the Louisiana, Mississippi and Alabama coasts, mainly from Tuesday afternoon through Wednesday. It's important not to focus solely on the location of the center at landfall, because impacts from wind, rain and storm surge will be felt well away from the center:
I believe it is important to emphasize that just because Isaac has remained at Tropical Storm strength until now, the system should not be dismissed as "weak" and taken too lightly. Intensification can occur very rapidly in this type of situation, and the developing core of the system is only now about to cross over the most warm and unstable waters of the Gulf of Mexico. For several days now I have been advising folks along the Gulf Coast to prepare as if Isaac will be a "major" hurricane by landfall, and I still feel strongly that is the best advice at this time.
Assuming the above forecast track verifies, the center of Isaac will be located to the Southeast of the City of New Orleans for a significant period of time from Tuesday afternoon through Wednesday morning. This is potentially very dangerous, as this means that a large amount of water (i.e., storm surge) will be pushed up by the counter-clockwise flow around Isaac right into the City, as well as adjacent portions of southeast Louisiana and southern Mississippi:
I am dumbfounded that the City of New Orleans has failed to issue an evacuation order through the time of this writing. I strongly encourage all residents of the area to take matters into their own hands and get to higher ground as soon as possible. Do not wait until its too late, as so many did almost 7 years ago to the day. Isaac is currently forecast to be moving at a slower pace than Katrina did, which will mean potentially that much more water being pushed up into the area in harms way for an even longer period of time. While I realize that the levee system has been "improved" since 2005, I am not confident that we should put the system to this kind of a test with so many lives at stake. Better to be safe than sorry. I'd say common sense should be the rule here. If you feel that you are in a vulnerable area, please get out now and do not wait for an order that may never come, or that comes too late once again.
Very heavy rainfall will also be a widespread threat with Isaac. Rainfall amounts in excess of 10 inches can be expected over a large area from southeast Louisiana into adjacent portions of southern Mississippi and Alabama:
Tornadoes will also be possible with some of the thunderstorms that spiral around the center of Isaac on Tuesday and Wednesday.
If you live in the Hurricane Warning area along the Gulf Coast (as shown in red on the NHC forecast track image above), you should rush your preparations to completion today. If you live in an area vulnerable to storm surge and other flooding, please have a plan in place to move to higher ground before Noon tomorrow at the latest.
For the latest imagery and updates on Isaac, please refer to this dedicated webpage at our sister site, WeatherGuidance.com. Now that the system is threatening the U.S. in the short range, I'll also be posting more frequent updates here on the blog. I will also post various shorter updates with additional images, etc., on both facebook and twitter. If you would like to receive those updates, please be sure to follow me there if you aren't already:
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