B-Bear wrote:otowntiger wrote:IN the NHC 5:00 discussion there was no talk of shear in the gulf like they've mentioned in the 5-6 previous advisories. Now they mention something very interesting, upwelling. That has never been talked about before now. I find it very interesting that suddenly there is no shear, but the water temps are now the issue. All along I've understood that upwelling would only occur where the storm sat for a long time and mixed up the deeper, cooler waters. I understand the SST's in the Gulf is a non issue, i.e. they are plenty warm. Anybody have any thoughts on that?
Here's how I understand it.
Upwelling will only occur if a hurricane is either stalled or moving at such a slow rate of speed that it allows water to pile up in front of it. Ivan is forecast to do neither of these things. Regarding the SSTs, I learned there are actually 2 factors--the SSTs and the heat content. SSTs are a measure of the surface temperature of the water, and the hurricane will build from that heat. The "heat content" is measure of the depth of the heat in the water. So with a high heat content, a hurricane might be more likely to maintain its intensity even with upwelling, since the water being churned up would likewise be warm. In the GOM there are very high SSTs, but the heat content is not generally that high. So if upwelling occurs, it might indeed affect Ivan's intensity. But that would only become a factor if he stalled or was moving very slow, and he's forecast to do neither.
I tend to agree with the previous poster's assessment. There is a monster hurricane about to emerge into the GOM and there are no predominant weather systems to definitively steer him. So the NHC sees that they have an out-of-control scenario on their hands and they are simply trying to keep people from panicking.
Thanks for the reply. I understand the upwelling process. I didn't know there were two measures of temperature, related to the depth. I know that Ivan is not predicted to slow that muc or stall and that is why I was surprised to see them mention upwelling. It not a factor for a storm that is forecast to be moving at least 10mph. What I am questioning now is what happened to the shear? Did they just forget to mention it or is it no longer forecasted? On the surface it would almost appear that they are just trying to come up with reasons for it to weaken. I don't think that is true, but I could see how it may look that way.
