Jul 31, 2011

DAY 61

There will be no 'E' storm in July this season as Invest 91L was unable to strengthen and close off a circulation today. A lot of times when we are talking about an area of low pressure in the initial stages of development, you hear the word 'broad' talked about quite often. In 91L's case, the word is 'elongated'. You can see from the satellite that it stretches all the way from the Antilles to about 48W.

There is actually a separate low that developed out in front of 91L a little closer to the original wave axis. That low has created a blob of thunderstorms and has its own circulation to it. Anytime in the past that we have seen competing lows like this, it stalls development until one is enveloped by the other. This is good news for those in the Antilles Islands because it will not be able to develop into a strong tropical system before impact there.

Models do predict that the primary low will eventually develop into Tropical Storm Emily within the next 24 to 36 hours. NHC is giving it a 90% chance of doing so. For most of the day 91L was listed with a near 100% chance of developing. These models will likely change quite a bit still because there isn't even a closed center of circulation yet. All indications are that this thing will eventually curve back out into the ocean. The key is when will it be able to do that. The computer models are taking this storm right up to the doorstep of south Florida before the hook, tracking right over the Leeward Islands and the Bahamas. That is likely why they are not forecasting a major hurricane to develop.

(Hurricane Charley's Track in August 2004)
If this system is able to stay below the Leeward Islands, we could see a track similar to Hurricane Charley in August of 2004. There is actually a similar setup. There is a ridge of high pressure over the continental US that would help block Texas and the Gulf Coast, and there is a trough that is forecast to drop into the north Atlantic. Just like the trough that lured Charley back across Florida.

DAY 60

Invest 91L is very close to becoming a tropical depression, and the National Hurricane Center is giving it a 90% chance of doing just that over the next 48 hours.  Late tonight it has lost some of its convection but that comes and goes with diurnal heating. It also looks like it has lost some of that spin that it has been exhibiting ever since it emerged from the African coast. But the low level vorticity is still there. There is still a little dry air and moderate shear around the system, but it is an environment that will allow 91L to continue to strengthen gradually.

Computer models are suggesting continual development as well. As for the guidance for 91L, there is an overwhelming consensus pointing towards the leeward Antilles. Its got a little more than 2 days before it gets there. That's probably not enough time to become a hurricane, but they will likely be dealing with a tropical storm there.

After that the models are all over the board. It is still far to early to make a call that far out. There is a higher probability as of right now that this storm will pull a Ralphy and curve out to see. But there is also several variables that could change these forecast tracks very quickly.

Jul 30, 2011

DAY 59

Landfall day. And I don't know what Texas did to piss off mother nature, but they kinda got jipped on the rainfall totals. Tropical Storm Don made landfall near Baffin Bay, Texas at about 8pm local time. And the same subsiding air that has plagued Texas for months, has now delivered a knock out punch to Tropical Storm Don. Almost immediately after landfall Don was downgraded to a Depression. You can see by this radar image that some places will be Lucky to even receive an inch of rain from Don.

Elsewhere in the tropical Atlantic the National Hurricane Center is watching a couple other areas. An area near Central America has been circled but given 0% chance of developing into a tropical cyclone in the next 48 hours. But the real focus is on the orange circle which is Invest 91L. That area has been given a 50% chance of becoming a tropical cyclone in the next 48 hours.

91L is a vigorous tropical wave that will be able to gradually organize in the coming days. It does have vorticity in all levels, in fact you can actually see some of that cyclonic action in the visible satellite. The environment is somewhat favorable for development. Upper level wind shear is light to moderate, which means that the dry air to the northwest of the system will be less likely to get entrained into its engine.

The computer models are quite enthusiastic about developing this Invest. These forecast tracks will change several times over the next few days, but it is intimidating to see them all pointing at the US coast like this. A couple of the models have this system as a tropical storm in as little as 24 hours. This should put the folks in the northern windward islands all the way to Puerto Rico on alert. Based on the current conditions and the forecast models, we could be looking at our 5th tropical cyclone in the Atlantic soon.

With just 48 hours left in July, the race for Emily is on. The last time we made it to the 'E' storm in July was the record breaking season of 2005 when we made it 5 letters deep into the Greek Alphabet. That year we even got to the 'G' storm in July when Tropical Storm Gert formed on July 24th. Lets not also forget that was the year of Katrina.

Emily herself is already a record holder. She is the only name, since 1979 when we added boy names to the mix and started the 6 year rotation , to have reached major hurricane strength 3 times. (Cat 4 in '05, Cat 3 in '93, Cat 3 in '87). If she manages to once again reach major hurricane status it will be her 4th such occurrence. In case your wondering, all time 2 other names have reached major hurricane status 4 times. Frances in 2004, 1980, 1976, and 1961, and Ella in 1978, 1969, 1962, and 1958.

Cat 5 Emily July 16th, 2005
Emily is also the earliest forming Category 5 Hurricane of all time. On July 16th, 2005 her central pressure fell to 929 mb and her sustained winds reached 160 mph.

Jul 29, 2011

DAY 58

Tropical Storm Don was able to strengthen just a bit today. And most of that strengthening occurred within the last couple hours. He continues on a WNW track towards south Texas with maximum sustained winds of 50 mph and his pressure is now at 998 mb. As of about 11pm tonight, Don was firing off some impressive convection with a last ditch effort to strengthen before his landfall tomorrow night.

Earlier today though you can watch Don's struggle to grow in this extended visible satellite loop. Through most of the animation you can see the low level spin exposed on the north side while most of Dons convection is removed to the south. This is a result of that northerly wind shear. Without the convection stacked vertically above the circulation, it is difficult for the storm to organize and grow. Also visible in this image are the low level Arc Clouds being spewed out from the northeast side of the storm, this is an indication that Don is swallowing dry air which also disrupts his ability to strengthen. Thus Don remains a weak tropical storm tonight

The official track from the Hurricane Center brings Don as a tropical storm into Texas just south of Corpus Christi in about 24 hours from now. Tropical Storm Warnings are in effect from Brownsville all the way to Galveston, although the northern sections near Galveston are no longer in the cone of possibility.

Rarely do you see people standing on the shore with open arms with the approach of a tropical system, but that's just what you may see tonight as drought stricken Texas is salivating with the possibility of heavy rainfall. You can see that most of the Texas coastline is in an Exceptional Drought.

It is tough to say exactly how much rain Don will be able to deliver. Often times tropical storms can dump more rain than a hurricane (Fay 2008). But that ridge that is responsible for putting Texas in the drought could zap some of the moisture potential from the approaching Don. He is not yet close enough to pick up any rain bands, but the National Weather Service on the Texas coast is expecting 1-2 inches widespread with up the 4 inches locally. That seems like a logical if not even conservative estimate especially if Don continues to move at 15 or plus mph.

The other feature in the tropical Atlantic that we are continuing to watch is the wave half way between Africa and the windward islands. It has now been dubbed 91L and given a 20% chance of developing into a tropical cyclone in the next 48 hours by the National Hurricane Center. The CMC is developing the system in 4 days and the GFS and NOGAPS are also acknowledging this system for future development. The next named storm in the Atlantic will be Emily.

Jul 28, 2011

DAY 57

Tropical Storm Don was born at 4pm eastern today just 2 hours after the National Hurricane Center released an advisory with a 100% chance of tropical cyclone development. At 2pm the system was so borderline that NHC decided to wait until the Hurricane Hunter recon mission was complete. They did find a closed center of circulation and sustained surface winds of 40 mph and Don was named.

Don will be hard pressed to become the seasons first Atlantic Hurricane. Atmospheric conditions are only marginally favorable for further development tomorrow. The forecast models have just started to come back around. I really don't know what happened to the HWRF and the GFDL. Both of them had this thing nailed on Saturday nights runs (as seen below) with a weak tropical storm just of the tip of the Yucatan valid for Wednesday night, and then NHC took 90L offline for almost an entire day. First it gives me great confidence in these 2 models to have nailed this one like that. But at the same time it worries me that they would lose it for a few days after that.

That's in the past though. As of 10pm eastern Don had sustained winds of 40 mph and a pressure of 1000 mb. He is continuing to move to the WNW at 12 mph. You can see that he has lost some of the convection that he had during the day and there still is no real obvious tight spin in Don. On the water vapor loop you can see that he is being sheared from the northeast and there is still is some dry air in front of Don.

The daytime heating of the Yucatan Peninsula may have caused some convective energy to be stolen from that area. But once he moves away from the landmass that wont hinder him any further. The only other factor is the vertical wind shear. From the shear tendency graph below you can see that there is only 5-10 knots of shear in his way, which is easily manageable. So with those factors Don should be able to slowly strengthen over the next 24-36 hours.

Model guidance for Don may change a little bit again in the morning once we get a good run that includes the recon data from earlier today. But for now they are pointing Don at the entire Texas coastline. The HWRF which has been steller on 48 hour track guidance over the past few years is leaning towards Corpus Christi and the GFDL is about 200 miles northeast near Galveston. In about 48 hours or so, on Friday night Don will likely make landfall on the Texas coast as a tropical storm. Don becoming a hurricane though cannot be ruled out just because the models are not taking him that strong. With the exception of the GFDL, they do take Don to the threshold of a Hurricane and he is in an area known for rapid intensification.

Elsewhere in the tropics there are 2 waves worth watching. You can see them on the surface vorticity map below. One is at the windward islands and could become our next invest, although there is no model support for this. (I've heard that before somewhere, lol). And a wave that came off of Africa yesterday that is now at 30w. That wave has received some attention from the global models for future consideration.

Jul 26, 2011

DAY 56

Invest 90L is finally taking the shape of a tropical cyclone. Located south of the western tip of Cuba with a lot of convection directly over the center of circulation. It also has some banding features around all sides of the storm.

90L is very close to becoming a tropical depression it will likely happen well before tomorrow night, it could even happen by 2am Wednesday morning which is the Hurricane Centers next scheduled advisory. The next step would be Don unless a surprise storm beats 90L to it. At their 8pm update, NHC was giving it a 40% chance of developing over the next 48 hours.

90L appears to have taken a slight southwesterly turn towards the Yucatan in the past couple hours. Now that the storm has started to revealed its true identity, the computer forecast models will be able to get a better grasp on the future of 90L. Most of the models do now develop 90L into Tropical Storm Don, but just barely. The HWRF is the only one that takes it to hurricane strength. As far as the tracks are concerned, there is no real consensus yet there. They are pointing from south Texas all the way to Louisiana. Until there is a closed center identified and the models will vary greatly. We should know more after the first recon flight into 90L occurs. That is scheduled for tomorrow.

So until tomorrow, at least we know now that there is a tropical cyclone in development and is likely headed towards the US coast.

Jul 25, 2011

DAY 55

90L is still alive tonight although the National Hurricane Center is giving it a 0% chance of developing in the next 48 hours. That's a fancy way of saying it has no chance. NHC even dropped 90L from it's designation for most of the day but brought it back online around 10pm. Based on that fact, I believe that they might raise its development probability a little higher by 2am.

It's not that this thing is about dead, it's just that it will still be more than 2 days before we see any development. There are several reasons not to stop watching 90L, besides the fact that you never stop watching a tropical system approaching North America. Below is the latest scan of surface vorticity which shows some increase in spin at the surface for 90L. Anytime you see that, there is a possibility for further development.

Another reason is the current runs of the intensity models like the SHIP are showing 90L becoming a tropical storm in 72 hours. These model seem to often overstep their bounds but it does indicate that there is something still in the works with 90L.

The GFDL and HWRF models were not run during the day because of 90L losing its designation. I suspect that these models are being run now, so we can check those out in the morning. Otherwise, all the global models are showing nothing from 90L what so ever. This should also be taken into account when forecasting the future of 90L. I will say that the GFS and the NOGAPS models were showing nothing what so ever while Bret and Cindy were busy becoming tropical storms.

Jul 24, 2011

DAY 54

Invest 90L had a ruff day but it is still alive. It's located near the Windward Passage between Cuba and Hispaniola. At one point today 90L had all of it's convection stripped away, but tonight those storms were able to refire. There is still no sign that this Invest is consolidating it's very broad appearance.

The Hurricane Center is still listing 90L with a 10% chance of developing over the next 48 hours. All the computer models are sending it into the Gulf of Mexico. 2 of the models shown below, the HWRF and the GFDL are showing 90L developing into a Category 1 hurricane on Wednesday as it impacts the northern tip of the Yucatan Peninsula. Though these models are similar they rarely agree that concisely with each other with location, timing, and intensity. Long term steering is showing a northward movement to this storm after that, we'll have to watch for a possible impact to Texas towards the end of the week.

Jul 23, 2011

DAY 53

90L is tracking right over the island of Hispaniola and looking a bit more formidable tonight. Showers from the system are widespread and disorganized however.

The Hurricane Center is giving it a 10% chance of becoming a tropical cyclone in the next 48 hours. 90L is dealing with unfavorable upper level wind shear and interaction with the island topography so development of this Invest is not expected anytime soon.

Most of the model guidance is taking 90L into the Gulf of Mexico were it is more likely to see development.

DAY 52

Bret is officially dead, Cindy is a depression and Dora is a minimal tropical storm. Invest 90L is the focus of the tropics at the moment. The Hurricane Center is giving it a 30% chance of becoming a tropical cyclone in the next 48 hours.

It has now reached the windward islands with the largest plume of convection over the island of Barbados. It is still a broad area of low pressure. A dominant low level center has not emerged yet however it continues to grow thunderstorms in the area.+

The models are not very enthused about this system at the moment. They've all kinda backed off except for the HWRF which develops a tropical storm once the waves makes it through the Caribbean and into the Gulf. It is a pocket of deep moisture within a very dry environment and until it takes on some kind of identity the model solutions will probably vary from run to run.

Jul 22, 2011

DAY 51

Bret has been downgraded to a depression with maximum sustained winds of 35 mph and a pressure of 1008 mb. He is expected to disappear by the weekend.

Cindy is still a tropical storm with maximum sustained winds of 50 mph and a pressure of 1000 mb. She built up to 60 mph winds for most of the day, but she is also expected to be gone by the weekend.

Hurricane Dora out in the Pacific registered maximum sustained winds of 155 mph (1 mph away from a Cat 5) with a pressure of 929 mb at the 8am update. That was as strong as she would get. Dora is the second Cat 4 storm in the Pacific already this season. Just now at the 2am update she has winds of 120 mph and a pressure of  953 mb. A Tropical Storm warning is in effect for the southern tip of the Baja including Cabo San Lucas.

The African wave we've been watching is moving closer to the windward islands and is still holding together. It is surrounded by dry air but otherwise has favorable conditions for development. The computer models have backed off in the latest runs except for the NOGAPS which is still developing a closed circulation when it reaches the Bahamas and then takes it into the Carolinas as a tropical storm.

Jul 21, 2011

DAY 50

Hurricane Dora is about as pretty as a storm gets. She is now a Category 4 major Hurricane with maximum sustained winds of 135 mph and a pressure of 948 mb. The good news is that the forecast track for now is away from the Baja Peninsula.

                                                 (Dora Loop)

                                              (Dora Visible)

Tropical Storm Bret is down to maximum sustained winds of 40 mph and a pressure of 1007 mb. He is still being heavily sheared from the north. The only convection is to the south of the center of circulation. Bret is forecast to continue moving out north-northeast and drop down to depression status tomorrow night.

                                                   (Bret Visible)

The Invest out in front of Bret has been named Cindy today. You could say that the Hurricane Center just wasted the name on a storm that will only live a few days and will have no impact on any land. You could say that in years with a high number of pre-season storms that are forecast, NHC will name borderline storms to help insure aggressive predictions. But most likely it was just a case of sticking to the 'letter of the law' and naming any tropical or sub-tropical storm that meets the criteria laid out by the NHC no matter how long or impacting the storm appears to be.

                                                 (Cindy Rainbow Infrared)

In this case Cindy deserves to be Cindy. She began her life along the same frontal boundary that Bret did. Once she broke free from that front, she was able to start using the ocean as the source of her energy and made the transition into a tropical storm. And Cindy is truly tropical. No one would fault you if you called her a sub-tropical storm though. After all she did form from a frontal system, and she did form in the sub-tropics and will never venture into the tropical latitudes. But in this case it's the center of circulation that makes the difference. You can see heavy convection right over the center of circulation indicating that the core of the storm is warm from top to bottom. A sub-tropical storm still has a cold level to it or would be completely cold-core and the center would be void of convection. The convection would be far removed from the center.

                                                (Cindy Visible)

But enough about Cindy already. We do still have the African wave that has been on our radar for a few days now. It is now at about 47 west and will be approaching the windward islands in about 3 days. Now all of the long range models have recognized this feature. The CMC, NoGaps, and the UKMet all develop a closed circulation in about six days and the GFS is at least now acknowledging the bend in the isobars throughout its duration. It is still to early to speculate on whether it will be able to stay below the many ridges to the north.

                                             (Atlantic Infrared)

Jul 20, 2011

DAY 49

Bret remains a tropical storm tonight with sustained winds of 50 mph and a pressure of 999mb. He is still headed north-northeast and is gradually starting to pick up speed, now moving at 8 mph. His forecast track has changed very little. Still no threat to land. Bret will continue to weaken, spending one more day at tropical storm strength.

Bret is being sheared from north to south. You can make out the fairly empty spin on this infrared image, and the only thunderstorm activity is on the south side of the storm.

The Hurricane Center has also circled another area of low pressure that has developed along the same old front that Bret was from. It has been given a 30% chance of becoming a sub-tropical storm. If by some strange reason it does develop it will receive the next name in line even though it will not be tropical in nature.

The strong African wave we've been watching is still healthy tonight. Some of its vorticity is not as clearly visible as it was yesterday but it is still producing lots of storms and carrying a lot of moisture along with it. The Canadian forecast model is still very aggressive in developing this storm as it makes its way into the northern Caribbean. It is still a long way out at this point. It could reach the windward islands by the weekend.