Tag Archives: Gulf of Mexico

Forecasting, Tropical

Emily Is a Threat To the U.S.

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After days of teasing weather watchers (and the National Hurricane Center), a tropical wave in the Atlantic has formed into Tropical Storm Emily.  The storm is rather disorganized and not at all “attractive” in the tropical cyclone sense, an artifact of its having had multiple competing vortices for several days that prevented its consolidation into a single system.

Because of its delay in getting organized, Emily is a threat to the United States.  I am going to blog regularly about this system as long as that remains the case.

 

What’s the synoptic setup?

Emily is going to move mostly west, slightly WNW, along the southern end of the Bermuda High.  Its strength will depend primarily on possible land interaction during this time.  The National Hurricane Center forecasts an impact on the island of Hispaniola, which would weaken the system.  How much remains to be seen; many a major hurricane has been reduced to a tropical storm by this island, but some systems that are much weaker have survived passage.  It is terribly difficult to forecast how much effect the mountains will have on any particular storm.  A lot depends on how well-organized the system is when it reaches the island (I do not mean its intensity; intensity and cyclonic organization are not the same thing), how long it stays there, and whether there are any additional destructive factors such as dry air intrusion and wind shear that are hitting the storm at the same time.  It is arguable that there’s not a lot of point in making a forecast for Emily after its interaction with Hispaniola at all, because what happens to it after that will be heavily influenced by its strength at that point.  I’ll discuss the various possibilities, however.

The high is going to be weakened on its left flank by a trough coming off the Atlantic coast in a couple of days.  This should pull the storm to the north.  How much depends on how weak Emily is and how strong the trough has managed to become.  The stronger Emily is, the more northward it is expected to move, all things being equal with respect to the trough.  I think that the trough will be the most important player here, though, and should be watched at least as closely as the tropical system.  It is very uncommon to have a strong trough coming off the East Coast at the beginning of August, and there has been a pattern this year of the GFS (the U.S.’s long-range weather forecast model) overdoing the strength of lows in the days before they arrive.  I am not inclined to buy into a strong trough unless I see it materialize, but it’s always best not to count anything out, either.

Emily is probably too far south and west to have a land-free recurvature (“fish storm”) path.  It’s not impossible, but it is unlikely.  It simply took too long to develop for that to be the most likely track.

 

What’s the model spread?

Models generally have clustered around the state of Florida as of Monday evening, with the NOGAPS (U.S. Navy model) farthest west and the GFDL farthest east.  The NOGAPS is showing an implied strike on the Florida panhandle (it has Emily stalling in the Gulf and not making final landfall within a 7-day period), and the GFDL shows a “fish storm” recurvature.  It is important to observe that this trend for the GFDL is relatively new; until the past 24 hours or so, that model was showing a strike on the East Coast of Florida and the HWRF model was showing a recurvature.  Now that has reversed itself.  In the meantime, the NOGAPS has been consistent in its Gulf track.  Consistency alone is not a reason to support a model’s output, but it is generally indicative of a model’s having a better grip on the environment than one that is prone to the “windshield wiper effect.”

 

Is the Gulf Coast at risk?

Short answer:  yes, but it’s not set in stone.  As of now, I still would say that the Florida peninsula is most likely to get hit, but the Gulf is a definite possibility, especially if Emily is weakened by interaction with land and/or the trough is weak.

Several forecasts indicate that the storm will remain weak for long enough to stay south and get into the Gulf of Mexico before making the recurvature.  This is not a fluke, or a one-off from some model; it has been a solution for the NOGAPS, Canadian, and UK several times over the past two days.  Furthermore, models such as the HWRF have been hinting at a Florida East Coast strike at a perpendicular angle, indicating a strengthening ridge that would force Emily westward again.  While these models do not go out far enough yet to indicate what would become of Emily after the Florida strike, entry into the Gulf (in a weakened state) is certainly possible in this scenario.

 

Forecasting, Tropical

90L: Weak and Into the Gulf

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The area of interest in the Atlantic, 90L, has become more likely to enter the Gulf of Mexico.  After a time yesterday when it was trying to spin up, the system has stayed weak and is now beginning to encounter land.  This land interaction will keep 90L weak as it passes through the Caribbean, making it even more likely to avoid the weakness in the Bermuda High that will be created by a trough.  90L currently has an area of moderate 700 mb to 850 mb vorticity associated with its convection.  This area of vorticity is what currently passes for a circulation.

It is important to note that, even though the current state of the system is less organized than yesterday and the National Hurricane Center has lowered its percentage of becoming a tropical cyclone in the next 48 hours (which I would completely agree with), 90L has gained additional model support for its long-term development prospects.  The cyclone-specific HWRF model was on board with 90L yesterday, taking it just south of Cuba and bringing it to 60 mph by the time it passes by.  Today the HWRF keeps the system even farther south, intensifies 90L to a Category 1 hurricane, and sends it into the Yucatan.  Additionally, the GFDL cyclone model, which was not doing anything at all with 90L yesterday, is today showing a Category 2 hurricane striking the Yucatan.  I think that is overdoing it, personally, but this system is showing indications of going into the Gulf of Mexico and intensifying then.

In recent hours, it has become possible that 90L is experiencing a center reformation.  The center has been located in the part of the system that is now south of Puerto Rico.  However, increased convection just south of Hispaniola (Fig. 1) is changing the polarity of the system, as is evident in upper-level divergence charts (Fig. 2).  This convection is likely associated with the mountains and therefore does not indicate improvement in the tropical structure of 90L.  However, if the center reforms to the northwest, this will throw a great deal of uncertainty into even the survival of 90L, as it will come much closer to the destructive mountains of Hispaniola and Cuba.  If the reformation does not occur, we are looking at a track like that of the GFDL and HWRF.  For my part, I am finding it hard to get on board with a center reformation over a more destructive environment that will make it hard for existing centers to stay together, let alone new ones to form, but time will tell.

One more important point to note for the GFDL model run is the strong ridge that would, in that scenario, serve to block 90L from moving north after it enters the Gulf.  The blocking ridge does not extend that far west in the HWRF run, making a Central Gulf landfall possible.

In summary:  90L is in a state of transition at present, and the outcome of a number of possibilities will determine its fate.  If the center reforms to the northwest, the GFDL and HWRF tracks should not be considered because they assume the present center.  The result of a reformation would be more land interaction, which means a weak system, delays in development, and the possibility of complete dissipation.  If the center does not reform, the GFDL and HWRF scenarios are in play, opening the doors for a significantly stronger system (and it should be noted that those models only go out to 126 hours, and have the system as an organized hurricane or near-hurricane in the middle of 90°F waters and low shear).  The ultimate landfalling location of 90L will then depend on the strength and extent of the ridge.


Figure 1: Rainbow-enhanced infrared image of 90L, Saturday evening.


Figure 2: Upper-level divergence over 90L.

Forecasting, Tropical

A Tropical System For the Gulf To Watch

A tropical wave, designated 90L by the National Hurricane Center, is worthy of being watched by the Gulf Coast states. This system is arguably the first tropical system of real interest to the Gulf states in the U.S., as Tropical Storm Arlene was regarded as a Mexican storm (correctly so) almost from its inception, and Tropical Storms Bret and Cindy were never a threat to any land areas.  However, 90L is in a situation that will strongly favor its reaching the Gulf of Mexico, where conditions are favorable for development.

The system has been steadily increasing its convection over the course of the day, and with this increase has come an improvement in its cyclonic structure.  Cyclonic curvature is evident on satellite (Fig. 1), and upper-level divergence (Fig. 2) indicates good ventilation for the system.  Lower-level convergence (not shown) is not so impressive, indicating that the system needs to form a strong low-level circulation to be considered a tropical cyclone.  This is usually the last step that developing tropical cyclones take.

90L is in a simple steering regime, being located south of the Bermuda High.  In about 3 days, a trough associated with a cyclone is expected to be located off the East Coast of the U.S., eroding the high somewhat.  It was previously assumed that this temporary weakening of the ridge would result in 90L being drawn north for a recurvature.  However, recently, it has become likely that the trough will be weaker than previously believed.  90L is also expected to take longer to develop owing to shear and likely land interaction.  The net result will be a stronger ridge and a weaker tropical system, and the consensus is that 90L will be forced into the Gulf of Mexico (Fig. 3).

90L will have to pass through an area of 20-knot wind shear (Fig. 3, Fig. 4), which is moderate, but will inhibit strengthening for as long as the system is located under that wind regime.  The GFS model does not indicate a sharp spike in wind shear over the course of 90L’s trek toward the Gulf of Mexico.

Unless the expected path drastically changes, 90L should enter the Gulf in about four or five days.  Models are unreliable for storms like this in the long range, and it should be noted that some of the models, like the GFS, are not particularly impressed with this system in the first place.  However, the cyclone-specific model HWRF does develop 90L into a 60 mph tropical storm, keeping it south of Cuba by the end of its run (126 hours out).  For my part, I am disinclined to accept a forecast of zero land interaction at this point.  However, the salient point is that any interaction with Cuba or Hispaniola will have a profoundly negative effect on 90L’s short-term intensity even if it becomes a tropical storm before reaching those areas, and avoiding those landmasses will result in a stronger cyclone that has not been delayed by a reorganization after being disrupted.

My gut forecast for a week or more out (in other words, break out the salt!) is that this system will become a tropical cyclone of moderate intensity (I’ll say Category 1, max, because of mild levels of shear in the Gulf even though the temperatures are well over 90 degrees in many areas) and that it will make landfall somewhere west of Pensacola.  I will have updates about this system if it continues to be a concern.


Figure 1: Shortwave infrared satellite of 90L, late Friday night


Figure 2: Upper-level divergence for 90L, late Friday night


Figure 3: Google Earth overlay of model tracks and shear for 90L, late Friday night


Figure 4: Wind shear tendency, late Friday night

Forecasting, Tropical

Tropical Depression 16 Headed to FL

As expected, the disturbance formerly known as 96L was classified today as Tropical Depression 16. The depression will probably strengthen to Tropical Storm Nicole. The models are forecasting the depression to get picked up by a trough and carried away as it becomes extratropical, with the GFS from 12Z indicating a rainmaker for most of the East Coast. (Lucky punks.)


This is impressive model agreement and indicates that they have a good handle on the strength of this trough.

Despite extremely warm water in its path, there probably isn’t enough time for it to strengthen into a hurricane, and shear associated with the trough is expected to increase before it makes its landfalls in Cuba and Florida. The SHIPS model shows a modest increase of 28 knots in the storm’s intensity before it weakens again.

In the longer term, this system—along with its predecessor, Matthew—probably heralds a shift in the type of tropical cyclone that will be forming in the remainder of the season, as well as the likely players that will be influencing the path of whatever does form. With the demise of the persistent ridge that brought the Southeast such oppressive heat for weeks upon weeks, and the establishment of a fall-like troughing pattern, we should see a greater threat to the Gulf Coast from anything that brews up—and, statistically, it is approaching the time of year when the Cape Verde conveyor belt shuts down and the tropical threat from “home-grown” systems increases. Additionally, this is a La Nina hurricane season; those have a tendency to start late and finish late, and by no means should the Gulf Coast consider itself safe from threats, including significant systems. In 1999, also a La Nina year, Hurricane Lenny almost reached Category 5 status in November. Even last year, during an El Nino, Hurricane Ida entered the Gulf in November and reached Category 2 status. We’re still in this.

Tropical

Dean strengthening, TD5 in Gulf

Good morning!

TS Dean has maintained its intensity of 45 knots overnight. Satellites from around 0900Z indicate that Dean is trying to wrap convection around an “eye”-like structure, which may in time develop into a true eye. The system has taken on the classic recognizable “comma” shape of a tropical cyclone, and in the face of low shear, should develop into a symmetrical and photogenic hurricane. Dean is in very low shear now, having escaped the 20kt that limited its intensification previously. This is good for development. However, since it’s happening during the day, Dean’s ability to utilize this may be limited. We’ll have to see.

NHC’s forecast has taken a westward shift, in line with what the computers are indicating. As I said in my previous blogs, I am on board with a Caribbean –> Gulf storm and do not intend to change this prediction unless the ridge is eroded too much for it to happen.

The GFDL and HWRF, our two tropical cyclone-specific models, are both in unfortunate agreement in their 00Z runs of taking Dean to a borderline Cat 3/Cat 4 in the central Caribbean and sending it south of Hispaniola. If this pans out, there is a chance that he will enter the Gulf as a Cat 3 or Cat 4 without ever having hit a large landmass.

I’m not happy about this. In such a scenario, we’d have to hope for shear towards landfall, because the very hottest Gulf waters are right offshore.

Closer to home, TD5 has formed in the Gulf, although according to the NHC it seems to have some problems getting together. Well, it’s a new system. That’s what usually happens. Quite honestly, in my opinion, TD5 could landfall in Texas as anything from a depression to (if conditions are perfect and it takes advantage) a low-end Category 1 hurricane. The NHC is forecasting a 40kt landfall. I think that, if TD5 gets organized in time, it has the potential for rapid development, and this forecast could be too low. With the depression, everything comes down to the timing of its organizing.

Climate change

Global Warming Would Drown the Coastal Hurricane Defenses

The barrier islands of the Gulf Coast are an important defense against hurricanes. Mostly uninhabited, they are the first landforms that a Gulf Coast hurricane strikes. While they do not weaken the hurricanes (they aren’t large enough), the islands take the brunt of the hurricane’s storm surge, diffusing it somewhat before the eye makes landfall on the mainland. They are also an important defense against tsunami, a real (if little-known) threat. Significant seismic activity has occurred in the Gulf of Mexico fairly recently.

Global warming is predicted to melt part of Greenland and/or West Antarctica, raising sea levels worldwide up to 20 feet (more if all of Greenland and some of West Antarctica melted). This would have horrific consequences on coastal cities around the globe, of course. This blog, however, will focus on one specific area — the United States Gulf Coast. (Ha, doesn’t it always?)

If global warming raised sea levels as predicted, most of low-lying Louisiana — as well as the critical barrier islands — would be underwater. The low-lying swampland of Louisiana, which has been receding for years now, is another natural barrier for the coast, as well as an environmental treasure. It too would be covered in water.

The coastline would lose its natural defenses against hurricanes.

And, as research is indicating, global warming would also intensify the hurricanes themselves.
The EPA produced a series of pictures showing the coastal areas that are most at risk from global warming-induced inundation. Red indicates areas that are less than 1.5 meters above sea level. The images can be clicked on to show a larger view.

Here is an image of Louisiana and Texas:

And here’s one of Mississippi, Alabama, and Florida:

It’s hard to see on these maps, but the barrier islands are the thin trail of red south of the main coastline. They would be underwater.

More disturbingly, from the National Environmental Trust, here is a QuickTime movie of how Biloxi, MS (and its barrier island) would be affected by a rise in sea level. (WARNING for dial-up users: 3 MB file!) I’ve linked to the movie from this graphic I’ve made showing how the coastline would be inundated.

The barrier island protecting the city would no longer exist. Sure, the projection of the land would still exist underwater, and would serve to slightly lessen the impact of a storm surge, but it isn’t at all the same as having a true island above the sea. A dry, projecting landmass stops the flow of water, at least temporarily, and breaks the waves. A former island that has gone underwater obviously doesn’t keep the water from flowing.

Also, as you can clearly see, the city itself would be partially underwater. This includes the glitzy new development that is taking place on this part of the coast in response to Hurricane Katrina — very shortsightedly, I ought to add. Whether this is because of the government of Haley Barbour, who is very likely a global warming skeptic, or because the businesses are aware of the risk but decided to hedge their bets, I do not know.

The Katrina recovery and rebuilding process is not taking global warming into account at all. When the next really bad hurricane strikes, its impact could be compounded by the effects of global warming. The coast will be farther inland due to rising waters, there will be fewer natural barriers, and the hurricane itself is likely to be stronger and wetter than it would be without global warming. And, as unfortunate as it is for me to say this, at this point it’s not enough to simply drive less, replace incandescent light bulbs with fluorescent, cross our fingers, and hope that we’ve stopped the problem.

I absolutely support cutting carbon emissions. If we don’t, the consequences will be even more horrendous than the scientists are daring to predict right now. But we’ve reached a point where it would be nothing short of grossly irresponsible to fail to look into preparation for the potentially disastrous changes that we have brought upon ourselves.

Tropical

Gulf Goes Nuts

July 19, 2005

July 19, 2006

That, I think, says it all.

This is exactly what worries me about this hurricane season. The entire Gulf can support a Category 5 now, and the East Pacific, despite being slightly cooler than the Gulf, has already produced the powerful Category Four Hurricane Daniel.

The rest of the ocean isn’t quite this warm, but it doesn’t really matter. As an example, Katrina entered the Gulf as a minimal hurricane and became a Category 5 as a direct result of low shear and boiling temperatures without entering any other body of water. Here is what the water temperatures looked like before Katrina’s entrance (using the same scale as the previous pictures):

The Gulf is clearly well on its way to this level.

The Gulf Coast, as battered as the infrastructure may be, must do something in preparation, and soon. There are people who still need housing. There are communities still struggling after Katrina. Parts of New Orleans remain a war zone.

Unless this season is extremely unusual, some spot on the Gulf Coast is likely to take a major hurricane strike in 60 days or less.

Please. Nobody wants to see yet another catastrophe.

Tropical

Gulf of Mexico resumes rapid warmup

For awhile, the seasonal warming of the Gulf of Mexico didn’t keep pace with the warming of 2005 (at the same time of year). That appears to have changed. It’s no real surprise, with temperatures near the Coast approaching 100 degrees in places and record highs being set on an almost-daily basis (the old records mostly having been set last year or over the past decade).

June 21, 2005: June 21, 2006:

Different regions are warming, definitely… and in fact, I’d recommend a comparison of June 2005 and June 2006. At this point last year, the Gulf was in a brief cooling trend. This year, it is in what can only be described as explosive warming.
June 2005 June 2006

(In other, completely, wholly unrelated news, yet another scientific study backs up the idea of human-induced explosive global warming.)

BTW, minor props to me for calling Alberto. Didn’t quite make hurricane status, nor do I expect it to be upgraded retroactively at the end of the season, but not too bad. At the end of the season, I’ll look over my various predictions and see how accurate they were overall.