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Monday, September 13, 2004 |
Weather comment []6:33:05 PM  trackback []
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| At 5 PM EDT, Hurricane Ivan was 30 miles south of the western tip of Cuba and moving to the north-northwest at 9 mph (with a resumed motion to the northwest expected later tonight). Maximum sustained winds remain 160 mph and minimum central pressure has fallen to 912 milibars (26.93") Initial motion is set at 330 degrees. This northerly motion is due to the trough. However, this trough is expected to lift, which would enable a northwesterly motion again. Hot on the heels of the trough lifting is another trough that would erode the ridge reestablished by the departure of the first trough. This would create another northerly motion that would then turn to a northeasterly motion. The forecast track remains to the east of model guidance. Regarding intensity, an observation from after the release of the advisory found central pressure to be 910 millibars. Slight strengthening is forecast in the short term and after that, increasing shear is expected to weaken Ivan. And as if Ivan weren't enough to keep the forecasters busy, Tropical Depression 11 was introduced to the world this afternoon... Weather comment []5:35:38 PM trackback []
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| The comments that follow are derived from my synoptic meteorology professor's comments upon the storm this afternoon. It seems that the models this morning had the trough 10 to 20 meters too shallow this morning. As Alan Sullivan noticed this morning, the trough has dug south of Louisiana (this can be seen on the water vapor imagery loop, notice how there is a flow towards the southeast that curves to the northeast around the corner of southeast Louisana. That is the trough). By having the trough too shallow, the models do not correctly grasp how far south it extends. This has major implications for the accuracy of their forecast. Another disconcerting thing that has been noted is how closely Ivan is passing to the tip of Cuba. The models and the National Hurricane Center forecast all had the center of the eye passing noticably clear of the tip. Less than six hours into the forecast, it already appears that the track is east of what was forecast at 11 this morning. While the error may seem small (and it is, probably no more than 20 miles) it can have big implications for future error. My reading last night from the Global Guide to Tropical Cyclone Forecasting covered this topic. Essentially, an initial error in position causes the amount of error in future position to double in each twelve hour period that passes. Troublesome stuff. Also, the heading of the storm appears to be have more of a northern component than anyone forecast at this point. Due to the trochoidal oscillatoins (wobblings) that occur with the movement of a storm this observation is a bit more subjective and prone to error. Nevertheless, it is another cause for concern. My professor that he would be drawing the cone of concern (ie areas that need to be mindful of a potential landfall) from Mobile to definitely Tallahassee, and probably all away around the Big Bend down to Tampa. He also said that he could see where Ivan could be strenthening some more. He based this off the sudden expansion of outflow to the north in the past two or three hours that is very noticable on ifrared satellite loops. It is worth noting that Ivan has not had the daylight hour weakening that has happened on previous days. NOTE: Any errors in the meteorology described here are my own (even when I say I'm quoting my professor. In those cases, any errors would be due to my misunderstanding and should not be attributed to him). It's about that time... so thus endeth this post. Weather comment []4:54:15 PM trackback []
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| What is shown below is something that "does not happen" and when it does, "should not happen". Here we see almost total agreement among three of the global models on the position of Ivan at a landfall 72 hours in the future. (The NOGAPS model run displayed is old... the 12Z run is a little bit to the right of the one displayed here). More often than not, when this sort of agreement occurs this far out, all of the models are wrong because they are making the same mistake. More to follow...  Weather comment []4:26:05 PM trackback []
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| At 11 AM EDT, Ivan is 85 miles south-southeast of the western tip of Cuba moving to the northwest at 8 mph. Winds remain at 160 mph and minimum central pressure is 915 mb (27.02"). The forecaster believes that the long anticipated turn to the northwest has begun and set the heading of the storm at 310 degrees. Ivan could strenghten slightly before encountering shear. Regardless, he's anticipated to make landfall as a major hurricane. I'm off to Atmospheric Dynamics, so I've no time to comment. Check out Fresh Bilge for his insightful commentary. Weather comment []11:01:39 AM trackback []
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| At 5 AM EDT, Hurricane Ivan was 120 miles south southeast of the western edge of Cuba and moving to the west-northwest at 9 mph. Maximum sustained winds are 160 mph and minimum central pressure is estimated to be 920 millibars (27.17") Shear continues to be a potential issue for Ivan in his near future. The forecaster shifted the track significantly westward (landfall forecast changed by about 65 miles), and would have shifted it even more west if there were not a previous forecast out. Weather comment []5:22:46 AM trackback []
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| At 2 AM EDT, Hurricane Ivan was 160 miles southeast of the western tip of Cuba and moving to the west-northwest at 9 mph. Maximum sustained winds are 160 mph and minimum central pressure is 920 mb (27.17") Weather comment []2:04:56 AM trackback []
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© Copyright
2004
Charles Fenwick
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Last update: 10/2/2004; 11:03:34 PM .
Last update: 10/2/2004; 11:03:34 PM .
