Texas probably safe, Jamaica not so much

Hurricane Dean remained a cat 4 storm with 145 MPH winds yesterday. This is a slight amount of weakening, but obviously still not a sunset walk on the beach. The news here is that it isn't a cat 5 yet, though that's probably in the cards for tomorrow, as the heat content of the northwestern Caribbean is immense. Dean is moving toward the west-northwest at 18 MPH; this motion is expected to continue basically for the next 3 days. Central pressure is 921 mb.

The forecast track has shifted slightly to the south today. Dean will remain a cat 4 storm as it rumbles through or just to the south of Jamaica during the day today. This is likely to be the worst storm to hit that island in many years. The Cayman Islands are next, but again, with the slight southward track adjustment, these islands might be spared the full brunt as Dean passes by during the early morning hours tomorrow.

Further out, the forecast model tracks have oozed slightly to the south, now cutting across the Yucatan and into Mexico. The threat to Texas is reduced, though I'm not yet convinced those residents need to completely drop their guard, especially along the southern coast.

It's headed right for us, mon!

Major hurricane Dean continued to roar across the Caribbean this morning. Maximum sustained winds are currently 150 MPH, which is a category 4 storm on the Saffir-Simpson scale. The threshold for a cat 5 storm is 155 MPH, and given the warm ocean waters and minimal shear ahead of Dean, it seems likely to become a cat 5 storm.

Dean has slowed slightly, now moving toward the west at 17 MPH. The short-term forecast remains unchanged; a direct hit on Jamaica seems inevitable. In addition to the usual effects from a cat 4 or 5 hurricane (wind, rain) mudslides induced by the mountainous terrain will add to the misery there.

Beyond Jamaica, the forecast is less clear. The forecast models continue to hint at landfall anywhere from the Yucatan to Houston. The models all differ in the way they model the movement of the upper-level areas of low pressure (currently over south Florida) and high pressure directly north of Dean. Another environmental sampling mission will provide new data for input into the forecast models tonight. This mission should help characterize these atmospheric features governing the movement of Dean. Still, there are no model solutions indicating a threat to Florida.

Models turn right

This morning, Hurricane Dean is a 100 MPH, category two storm, racing to the west at 24 MPH. Dean is currently located in the channel between St. Lucia and Martinique. The storm is fairly impressive looking on satellite, however, the radar presentation from Martinique radar indicates less organization than one might expect.

As mentioned yesterday, the environmental sampling mission was flown to measure atmospheric conditions around Dean and input these data into last night's forecast model cycle. The models have responded to these new observations by generally making a slight turn to the right in the 3-5 day forecast range. The models in this case are weakening the western edge of the high pressure ridge north of Dean. These forecast tracks indicate an increased risk to the western Gulf coast, e.g., Texas and western Louisiana. Some models still indicate the southern route into Mexico is preferred. Nothing is certain yet, but now we simply have a slightly larger error cone than we previously did. We still don't have a model run indicating a risk to Florida.

Not much change to our expectations of the peak intensity: we still cannot find a good reason why Dean should not become this seasons first major hurricane, and category 4 strength (131 MPH) is not out of the question.

First hurricane of the season

At the 5 AM advisory this morning, the Hurricane Center upgraded Dean to a hurricane, making it the first one of the season. He is a minimal hurricane, with 75 MPH winds, and is moving toward the west at 24 MPH. Hurricane warnings have been hoisted for the islands of Dominica and St. Lucia, and a variety of other watches and warnings have been issued for most of the remaining Lesser Antilles. Hurricane conditions are expected in the warned area within 24 hours. The Hurricane Hunters are planning to fly into Dean today.

Taking the longer term view, the modeling of Dean's future track remains in excellent agreement. None of the models track Dean north of Jamaica, and many of them move him into the Yucatan at day 5. In other words, they're all rather far south of Florida. This, of course, is subject to change. In fact, there could be a bit of model gymnastics (flipping and flopping) by this time tomorrow; in addition to the Hurricane Hunter mission, NOAA is planning to fly an environmental weather data sampling mission tonight to provide additional observations for input to the models. Model accuracy typically increases when these data are ingested, and occasionally we see some, ahem, interesting changes in the track.

The primary features governing the steering currents are a dome of high pressure directly to the north of the storm, and an area of low pressure over the Bahamas. You can see these features in this water vapor satellite loop (warning: link is not safe for dial up). Both of these features are forecast to move toward the west, such that the low would not pull Dean to the north while the high pressure dome would persist the westerly track into Mexico. The sampling mission tonight is designed to provide data to more accurately describe these features. If the low doesn't move as expected, the western Gulf of Mexico coast comes back into play early next week.

Intensity forecast remains straightforward. Based on our current knowledge of hurricane intensity change (which, admittedly, at times doesn't seem like we know very much) there appears to be little reason for Dean not to intensify over the next 5 days. No interactions with land or wind shear are expected, and the ocean temps are warm. Forecast to major hurricane strength is expected.

Tropical storm Erin is forecast to move onto the Texas coast sometime in the next 12 hours. Biggest threat is flooding from the 3-6 inches of rain expected there. This is a part of the country that does not need additional rain. If the current modeling is to believed, this area may get another dose of tropical rain next week.

Both of our areas of concern have strengthened since yesterday. First is the newly formed TD5 in the Gulf of Mexico. It's having some organizational issues at this moment, which will probably preclude any significant strengthening despite a decrease in the vertical shear in the vicinity. Landfall is expected as a tropical storm in the next two to three days along the Mexico/Texas border.

Tropical storm Dean was upgraded yesterday. Upon its upgrade, it promptly began to weaken for the next 6-9 hours. A strong convective burst overnight can be seen in the satellite imagery, so one would expect the weakening trend has ended. Currently a 50 MPH tropical storm, strengthening should continue as the easterly shear is decreasing, and the storm is moving toward increasingly warmer water temperatures. A slow, steady increase in strength is expected over the next two to three days. Dean is moving primarily toward the west at 18 MPH.

To the extent one can believe 6-9 day hurricane track forecasts, the forecast track has clarified somewhat. The modeling is by no means complete, as some of the models are still shaking out some of their problems locating the storm center correctly. However, most of the recent modeling takes Dean into the Caribbean; that is, south of the Greater Antilles, instead of north of these islands. The idea of a landfall along the east coast of the US has, for now, been discarded. A dome of high pressure is expected to be along the north edge of Dean for the next 3-5 days, which will induce a general west to west-northwestward motion. This dome of high pressure should "protect" the Florida Peninsula from a direct hit. Current thinking which, of course, could change, has Dean exiting the Caribbean in the general vicinity of the Yucatan Channel (between Mexico and Cuba), with an ultimate landfall along the western Gulf coast to, perhaps, as far east as the Florida panhandle.

The intensity forecast remains a little easier than the track forecast. The shear is weakening, and the environment is favorable, so Dean should be a hurricane in the next two days prior to landfall in the Lesser Antilles. Once entering the Caribbean, Dean has everything going for it, such that it should become a major hurricane.

Hurricane climatologies (i.e., past storms) indicate that storms that form in the general vicinity of where Dean formed and then pass 60 west longitude south of 20 north latitude generally make landfall in the US or Mexico, and generally became major hurricanes at some point. Since it seems likely Dean will cross 60 west at or near 15 north, these climatologies indicate an interesting week ahead.

Clearing out the cobwebs

Wow...50 weeks since the last time I made a post. One side effect of a quiet tropical season is that I have to clear all of the cobwebs off of the blog that have accumulated over the past year. Not that I'm complaining though...more cobwebs means less tropical activity to be concerned with.

There are two areas of concern this morning. The first is in the Gulf of Mexico, where a area of low pressure is gaining organization just north of the Yucatan. This region isn't a depression or a named storm yet, but could be in the next day or so. The Hurricane Hunters will be flying into this disturbance later today. All modeling indicates this will head west toward Mexico or southern Texas, and shouldn't impact Florida.

The second area of concern is Tropical Depression 4 out in the open Atlantic. TD4 is currently located about 1660 miles east of the Lesser Antilles, is moving smartly toward the west at 21 mph with maximum sustained winds of 35 mph. It could be upgraded to a tropical storm later today. Now, we generally don't concern ourselves with tropical depressions 1700 miles east of the islands. However, this one is fairly interesting, as it's one of the few cases where we're more certain of the intensity forecast than the track forecast.

The intensity forecast calls for small strengthening over the next 2-3 days. Currently easterly shear is blowing the developing thunderstorms off to the western side of the circulation center. This shear is forecast to relax , and TD4 is expected to hit warmer ocean waters, so the forecast calls for TD4 to be a minimal hurricane (75 mph) at 72 hours (early Friday morning). Further strengthening is forecast after three days, but since the intensity forecast is obviously coupled with the track forecast, and since there are considerable uncertainties in the forecast track, it's probably best not to worry about that just yet.

The forecast track is more uncertain than usual. Currently, some computer models take TD4 into the Caribbean, while other models take the storm north of Puerto Rico. US landfall points range from Texas to New England if the modeling is to be believed. The differences will hopefully shake themselves out of the modeling system over the next couple of days. Many of the models have not started with the correct initial conditions of TD4, and if the model doesn't have that correct, it's difficult to produce a good forecast. The official forecast takes TD4 just to the north and east of Puerto Rico in 5 days (Sunday), which follows the large majority of the computer guidance.

So, what does it all mean? Now is the time to begin to check that hurricane supply list to see what you've got and figure out what you need. Certainly this isn't a time to panic; if TD4 is heading this way, it probably won't be here for another 8-10 days, so you've got time.