Unless you're a newby to Daily Kos, you know what these updates are about. I've been less active in the political discussions of late on dKos, as I needed a break. My energy was sapped after the 2008 election followed by a series of gay marriage battles/storylines (Prop 8 challenges and decisions, Iowa, Maine, New Hampshire, etc). But, with the 2009 hurricane season coming to life, I wanted to resume my updates for the dKos "family".
Note: While most of the community here seems to like these diaries, I am sensitive to some of the criticism (these are non-political and, thus, "off-topic", or these can lend to confusion, not assistance, if my forecast differs from the National Hurricane Center's). These critiques are not unfounded, but we hashed them out last year and the consensus, I think, was to continue these forecasts. So, that's what I'm doing. So, now, on to it...
For the newbies to dKos, a brief bio: I am a meteorologist who has been in the hurricane forecasting business (as well as other fields within meteorology) for over 15 years. Maybe I'm good, maybe I suck... I dunno... I leave that to the judgment of the readers. But the bottom line is that I'm trying to provide information to the dKos family that will, I hope, serve to make people better informed and, in turn, better prepared for any possible incoming storm. So, let's get to it...
First an intro on the 2009 season. I've heard a lot of chatter about how the East Coast and especially the Northeast is under the gun this year. I've heard this many times in previous seasons and, inevitably, it's pure and total b.s. This year is the exception. I performed a pretty extensive analysis of past hurricane seasons with storms in the Northeast. You can get the historical tracks from this Unisys site, to determine which years featured hurricanes in the Northeast (1938, 1944, 1954, 1960, 1976, 1985 and 1991 are the most notable in the past 100 years... there were a couple of other more marginal strikes as well). Looking at those seasons you'll find that most of those were accompanied by cool early summer weather in the Northeast. Also, contrary to popular belief, these were also decidedly normal seasons (or even slightly inactive). The standard thinking is that you need an active season to get a hurricane in the Notheast (the simple idea that more storms = more chances). This is untrue... more storms is due to warmer Atlantic water (that is the #1 correlator to Atlantic activity); this is, in turn, usually due to weaker trade winds causing less upwelling. Weaker trades are, in turn, generally the result of a weaker subtropical ridge (a big high pressure in the middle of the Atlantic). Hurricanes usually ride around the periphery of that ridge; so, if it's weaker, the storms will turn north at a further east longitude - striking Bermuda or missing land altogether. Not a single one of the aforementioned Northeast storm seasons was an active season.
...in short, for a change, the hyping of Northeast, or even just East Coast (since most Northeast storms also clip the Carolinas) storm potential this season is very real. Of course, there have been plenty of normal activity seasons with cool early summers that yielded no Northeast storm activity. So, there is absolutely no certainty here... merely that the risk is higher than normal this year.
Now, as for Ana and Tropical Depression #3, there is actually not a whole lot to discuss, as the model guidance is pretty well clustered for the next 5 days. Both storms will move west to westnorthwest throughout the period, and both storms should undergo some slow strengthening. And that motion will make both storms a threat to the northeastern Caribbean and probably to the U.S. (though most models now insist that TD#3 will hook out to sea just in the nick of time).
First, Ana. Here's how she looks this afternoon:
...you can see from this satellite image that this is a pretty modest storm. It doesn't really have any resemblance to a classic hurricane. However, note the deep convection (the brownish colors) in the middle. This is generally a "healthy" sign for a storm, especially since this convection is right over the center of Ana. Previously, any such convection had been ripped off to the west, as Ana was under easterly wind shear. Now, conditions have improved, the convection has developed over the storm's center, and the system has gone from being declared dissipated (yesterday), back to a depression, and now up to tropical storm status today.
So, where is Ana headed and how strong will it be once it gets there? Well, here's what the National Hurricane Center says:
...they have Ana clipping the northeastern Caribbean islands as a tropical storm, then approaching south Florida on Wednesday - also as a tropical storm. I will generally only vary from the NHC when I see good, solid reason to do so. There isn't any today. Here's where the models track Ana:
...Looking at those models you may think that NHC is leaning rather far north, and that a more southerly track would be reasonable, especially considering that Ana has generally tracked south of previous expectations (back when it was a depression over the past few days). However, note the legend; those three southern tracks are GHMI, GFTI and GFNI. Those are all perturbations of the same model. All of the other models are in that northern cluster. So, that basically seems more reasonable and is very much in line with NHC's track. So, as far as I'm concerned, they're right on with this one. As for Ana's intensity, I didn't pull the intensity image from Alan Huffman's web site, but there is much spread in the model guidance. However, the historically best guidance is in the 60-75kt range by 120hrs. That would put Ana at minimal hurricane strength when it approaches Florida. That's a bit stronger than NHC depicts, but, here again, I'd side with NHC... with one caveat. The caveat is that intensity is tricky to forecast, and Ana should at least be near hurricane strength in five days, so I absolutely would NOT be surprised if it gets to hurricane strength. But, for now, I'd side with NHC, keeping the storm just below that. The reason is that Ana may encounter more shear, precluding significant development. Also, often times in the early development stages - like now - the intensification rate can be slower than models project, because the system is still organizing. That does not always hold true, but I think it's true in this case. That means that Ana will get a bit of a slow start intensity-wise, allowing for less time to reach hurricane strength.
So, NHC says a strong tropical storm into south Florida in five days, and that looks about right to me. Keep one thing in mind, however... beyond about day 3, hurricane prediction is notoriously poor. So, we'll just have to keep closely monitoring Ana as the hours and days go by.
Now, as for TD#3. It will very soon be Tropical Storm Bill. I'll be shocked if it's not. Here's how the system looks now:
...structurally, with the "banding" features (esp. on the south side) TD#3 actually looks better than Ana. However, TD#3 does lack sufficient convection near its circulation center. So, it may be just below tropical storm strength, as NHC has it, but it is clearly right on the cusp. This could become Tropical Storm Bill at any time.
And where is this one headed? Again, NHC is all over it, IMO. Here's their forecast:
...and here are the track models...
The track models are in near perfect agreement (the stray purple line is the irrelevant "extrapolation" line), and NHC is projecting TD#3 to run right down that corridor. That brings it to near the notheastern Caribbean as a hurricane. NHC puts TD#3 at 90kts at that point. The best guidance (again, not shown here, but you can find it at the Huffman link above) is clustered right around that 90kt mark. So, once again, I can find no reason to stray from NHC.
What about the U.S. potential impacts from TD#3? Well, that is more sketchy. The basic problem is that it's just too far out; not all of the details of the evolving weather pattern are nailed down just yet. Moreover, the hurricane models don't go out that far. So, we're stuck looking at three long-range, global models:
The first, run by the American government (known as the GFS) keeps TD#3 out to sea, but in a close call (but not close enough for major coastal impact). The timing is early the week after next (around nine days from now). The second, run by the Europeans (known as the ECMWF) and the third, run by the Canadians (known as the GEM) are even further east. But all three are close enough to New England such that, being 6-10 days out, it must be monitored closely when it gets a little nearer.
I'll leave it at that for now, but I should add, regarding Ana, that there is also a Gulf issue. The forecast takes the storm to Florida in five days. But then where??? There is little model guidance on this, but what there is generally indicates that Ana will move into the extreme eastern Gulf then hook hard north, into the Florida Panhandle or the Florida Big Bend area. Like TD#3, that's just too far out to make any accurate guesses on... but suffice it to say that the eastern Gulf could be threatened by TD#3 as well.
That's all for now. I'm not sure if I'll be able to update as frequently and extensively this season as I did last, but I'll try my best to keep you all up to date.
UPDATE: 5PM EDT, the National Hurricane Center has shifted the track for Ana slightly south, avoiding landfall in south Florida (albeit barely, so south Floridians shouldn't take much comfort in this). And they have also, very expectedly, upgraded Tropical Depression #3 to Tropical Storm Bill.