| I think that's why they had it as a remnant low for the entire 5 day forecast period on the advisory where they downgraded it. They were at least trying to indicate it had a good chance of sticking around. Depressions though are tricky. What wind speed makes a depression? The very fact that there is no official wind speed minimum means that they don't have to use strictly the satellite data. I rarely saw a good Quikscat pass when I wanted one, so I'm not sure what the estimated winds were from the satellite. I do think at some point an area that is well organized, but mostly devoid of significant convection, should be downgraded. I think they should let it go for awhile, which they did. From the advisory that originally downgraded TD2 to a remnant low: "INDEED...IT HAS BEEN ALMOST 24 HR SINCE ENOUGH ORGANIZED CONVECTION EXISTED TO GET A DATA-T NUMBER." I think they were really trying to give it a chance because they realized it definitely had a shot at continuing. However, at some point, with mets pointing to the area on screen, it was getting to the point where it was mostly a swirl of clouds with only a thunderstorm trying to fire at the center. Looking at it on TV, it looked odd that it was still a depression. I realized what they were doing, trying to give it a chance and not look at short term changes, but at some point that became a long term change. For people watching at home seeing a mostly naked swirl, it might make some people wonder if it really is anything and if they can really believe what they are seeing. (and you could probably tell from an on air met whether they believed what they were seeing) That is where we get back to how should these areas be treated? A moment type deal where whatever seems to exist at the last available observation time is what you go with, or look at something averaged over time, where you look at a trend. I think they played it pretty well. If it was a moment type deal, they would not have went about a day without their satellite intensity estimates. Anything more than a day of a naked swirl (or close to it despite that persistent center that spawned some convection) that was a depression and it starts becoming a little odd when they keep saying we expect it to become a named tropical storm and yet it doesn't and simply looks good on visible but just doesn't look like much on water vapor imagery. Now they could have handled something differently, which is what you might be saying. There is no minimum wind speed for a depression. So by definition there is some increased subjectivity not being associated with the Saffir-Simpson hurricane wind scale. They could have said it was a 25 knot "depression" still and simply not have it strengthening. They actually did do that in the advisory prior to when they downgraded it to a remnant low. They could have let that go for a little longer I guess. Then it just comes down to once again, what is a tropical depression? What does the public think a tropical depression is? Should that matter in the decision to keep it a depression? If it has a good change of regeneration, should that be a factor? That is why I don't like a lot of subjectivity. You can get one person to say one thing and have someone else think something else. I want something official that can be quantified. But when they are weak it doesn't matter as much with a little more subjectivity. But the term "remnant low" is a little confusing. The same is said of storms that are off to the big Atlantic graveyard to the North. "Remnant" seems to indicate adios without further clarification from an NHC discussion. The ATCF database describes something as a "Low" instead rather than adding a "remnant" before it. I guess perhaps we could clarify a depression to be a closed circulation would any persistent convection at the center over a certain period of time that is 33 knots or less and then say after so many hours it is a "low" or "remnant low" if there is no more convection fired. The NHC describes a tropical cyclone as: "A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects)." Very subjective. Here is the definition of "remnant low": "Used for systems no longer having the sufficient convective organization required of a tropical cyclone (e.g., the swirls of stratocumulus in the eastern North Pacific)." This of course wasn't a simple swirl with no shot which is what "remnant" sounds like, but it also did not necessarily meet the "organized deep convection" standard. Or did it with some persistent convection at the center? I see a no win. They thought it had an opportunity to strengthen and it didn't, so I can't blame them for not getting that part right. (And so you would have some that would lose confidence in them because they kept saying it would strengthen and it turned out not to after it being mentioned again and again.) Would people take the storm less seriously later with it having been mentioned for a day or two as going to strengthen but didn't? Or would they forget about that? Or would it be better to drop it and not have it mentioned with a forecast and therefore have no expectation other than to watch it and see what happens and if they re-initiate advisories then people would not tune out but pay attention because it has become something once again. Since there really is no standard, I think they did good here. They mixed satellite data with human interpretation. Perhaps they could have a depression be something showing any signs of convection at the center, something a system proving to be vigorous might have, whereas a naked swirl off to the graveyard would be a remnant low where "remnant" had the sound it intends, that it ain't coming back. |