| Clark |
| (Meteorologist) |
| Fri Sep 05 2008 08:00 AM |
Re: Hanna Approaches Carolinas, Ike Remains Major
|
Quote:
Another rookie question, can the Doppler radars be ramped up in situations like Hanna to learn more about her make up, she is far off our coast ( further than current radar readings of < 120 km) . I think I remember a time about a month ago when Melborne was under repair and that Tampa seemed to take over a good chunk of CF. Maybe looking at Doppler radar is only entertaining for us lurkers, I read the Doppler tutorial, but still didn’t understand if the readings help the NHC or not. Is it all about the recon, if so why? I do remember hearing about the crappie Cuban radar, so it must mean something. And the (‘drops downs’do what the radar can’t. You seem pretty excited about airplanes going out to see big bad Ike, tell me why that is so important. Can we learn if the radar ramps up? Did we learn? Is that why NHC is doing better in path, but wants nothing to do with strength. i.e. Ike T.S. puff H3..h4.
As others have mentioned, Doppler radars are limited in range by the curvature of the Earth. They are also limited in effectiveness by time considerations (e.g. for emitted pulses to be returned to the radar before the next scan takes places), the base elevation angle (0.5 degrees, which doesn't sound like a lot but leads to overshooting a lot of stuff over 100 miles away from the radar), and their power. Tampa's radar (and also Melbourne's) can cover most of Central Florida because of the narrowness of the peninsula and thus relative proximity of the radars.
Radar analyses help the NHC from the standpoint of gauging storm structure -- eye, eyewall, etc. -- and diagnosing its winds using Doppler velocity data. While they are not surface winds, those data can be converted to approximate surface winds and used to better diagnose the storm's current intensity. Aircraft recon also have radars from time to time, though those are mostly used in research modes rather than real-time forecasting operations.
Recon flights are so important because they have tools that allow us to measure surface winds (the SFMR tool), gain an understanding of the storm's vertical structure (dropsondes), and gauge its intensity in a way that we cannot do with any other tool such as radar or satellite.
Ultimately, the NHC intensity forecasts have not improved much in skill over the years because we can't accurately represent what is going on within the storm at all times. We just don't have the full knowledge that we need, nor do we have the computational power to take what knowledge we have and make an accurate forecast. We know conditions that are favorable and those that are unfavorable, but we can't always judge how those will evolve in 12 hr, yet alone 120 hr. Intensity change is such a fine-scale, highly non-linear process that it makes its predictability quite the chore. Track forecasts, however, are largely dependent upon larger-scale features, features that are well understood, analyzed, and predicted and have become increasingly so over the years. Thus, we see large improvements in track without large improvements in intensity even considering that track forecasts are dependent upon intensity!