Monthly Archives: August 2011

Hurricane Katia

A large tropical wave near the Cape Verde Islands had been tagged as Invest 92L and upgraded to Tropical Depression Twelve and later was upgraded to Tropical Storm Katia by the NHC. Tropical Storm Katia as had excellent cyclonic turning before it even exited the coast of Africa. Katie is a well organized system, and is well is the process of developing an excellent Central Dense Overcast (CDO) and in fact is becoming more symmetrical via satellite presentation. Katia is moving at a fast clip of 20 MPH and has pretty much stayed on the 285 degree (WNW) track with a few wobbles now and then. An upper level low to the NW of Katia may, in time, become a role in the intensity of Katia, but should be a hurricane within the next 12-24 hours. The same upper level low may also induce some southwesterly shear, possibly within 96- 129 hours. At the same though, weak vertical shear and warm SST’s may be able to overcome the shear and allow further strengthening.
EDIT: As of the 11pm advisory tropical storm Katia has been upgraded to Hurricane Katia

Although it is way to early as to where Katia will be heading in the long term forecast, here are 3 trains of thought.

  1.  Katia stays west and heads into the Caribbean and is a threat to the western Caribbean and possibly later into the GOM.
  2.  Katia continues its WNW and either is a threat to the Lesser Antilles or is north of the Antilles and later turns NW toward the US coastline.
  3. Katia continues its WNW track, then NW, and eventually heads north possibly threatening Bermuda and even possibly heading into the Canadian maritimes or even recurves out to sea threatening no one.

Another fly in the ointment is an area of low pressure near western Cuba (now tagged as Invest 93L). That area possibly may develop into a tropical cyclone. This may have implications as to where Katia may head later in the forecast period.

Scenario 1 where Katia stays in the Caribbean, has a very low chance, maybe 10% and thats being generous. Katie is already at 14.4 °N latitude and slowly gaining. Unless something drastic happens, I just can’t see that scenario 1 will ever play out, but I don’t want to rule it out.

Scenario 2 where Katia possibly threatens the Lesser Antilles or is 100 miles north of the islands, this has maximum of a 30% chance. If Katie has not made the turn from WNW to NW then this scenario might happen. The trough that is forecast is either to weak or pulls out early, this may allow Katia to head a little further west than forecast. It also is dependent on that area of low pressure in the southern GOM has developed into a tropical cyclone or not (I will allude to that later).

Scenario 3 – recurving and not hitting the eastern coast of the US but possible impacting Bermuda. This scenario has the highest chance – 60% chance. At this moment, most of the models are very much in agreement. Katia should begin to turn to the northwest and eventually turn north because of the trough that will situated over the eastern US by Monday of next week.

Assuming that scenario 1 is out of the picture , lets visit the area of low pressure in the southern Gulf (93L).

In the Eastern Pacific, the western Caribbean and into the southern GOM, along with an old frontal boundary that runs along Florida to the western GOM, a surface low may be trying to form possibly to the north of the Yucatan. Some models are supporting this and this may head NW toward the Texas area. The oceanic heat is very warm in this area (in some areas, 30°-31° Celsius) and a depression or tropical storm (Lee) most likely will develop. The ridge over Texas is still strong but a shortwave trough might have enough punch to create a weakness in that ridge in a few days. As the trough gets closer to Texas, this may cause the 93L to stall or drift for a few days. Even if this system does not have “landfall” in Texas, this may create enough rainfall to help the relief in that area.

Back to Katia, and scenarios 2 and 3. If 93L develops to become a named storm “Lee”, then a ridge would be in place in the west central Caribbean. With 93L in the Gulf, Katia in the Atlantic and the ridge between the two, this would be enough to force Katia northwest and should keep Katia from the eastern coast of the US or at least the southeast coast.

GFS Model at 168 hours

ECMWF Model at 192 hours

Again, this is just a long term forecast – which ever scenario plays out – all of them will have changes in them. As always, remember to always use the official information from your local NWS and the NHC.

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Powerful and Dangerous Hurricane Irene

As the Bahamas got pummeled by Hurricane Irene with some Category two and Category three winds with hopes that damages would be minimal and no one has lost their life, all eyes are looking at Hurricane Irene’s next target, North Carolina and all points north. From the time Irene began it’s turn from the coast of the Dominican Republic, into the southern Bahamas and the eye wobbling (Trochoidal Oscillation) towards the Bahamas different islands, it was apparent that this was going to be one of the most dangerous hurricanes in a long time.

Irene near Dominican Republic/Haiti & Southern Bahamas – 08/23/11

Thankfully, those who live in Florida were being spared as Irene was just offshore a hundred miles or so. Florida had been and continued to have just some breezy winds and a few outer rain bands as Irene continued it’s trek northwestward. Although it took a while to do so, Irene began it turn to the north-northwest.

The latest steering current layer for Irene is now showing that the subtropical ridge has strengthened a little thus it has moved slightly allowing the weakness in the ridge to also move a little to the west. The trough had kept Irene on a north or north-northeast track. Currently, Irene is on a north-northeastward track which keep Irene heading toward North Carolina and the Outer Banks. Unfortunately, the ridge will continue to be there as as Irene heads toward Delaware, Long Island, and upward and this will keep Irene on a north-northeastward track. The most models are very much in a consensus and are very tightly clustered and a curvature out to sea is not indicated.

Steering Current

00z Dynamic(Early) Models

00z Dynamic(Late) Models

Currently, light to moderate southwesterly vertical wind shear along with some dry air has made it slightly difficult for Irene to strengthen but at the same time Irene will be in 28°-29°C SST’s so some possible strengthening may occur.

As Irene approaches the Outer Banks of North Carolina, some slight weakening may occur so Irene will either be a Category 3 or Category 2 Storm. Irene should begin a weakening phase after leaving North Carolina as it heads towards the Long Island area. By the time Irene moves into New England, Irene will weaken very quickly and under goes the extra-tropical transition phase.

By now all those who will be affected, especially those on the Outer Banks and North Carolina have evacuated their homes and into safe shelters.

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Tropical Depression Ten

The tropical wave south west of the Cape Verde Islands had been tagged as Invest 90L but has been upgraded to Tropical Depression Ten as of the 5:00AM advisory from the NHC. The environment for Tropical Depression Ten is somewhat favourable for continuing development and a tropical storm may form within the next day or two. A few of the models show a possible tropical storm may develop. Most of the models also are supporting a track toward the northwest but by day 3 or 4, Tropical Depression Ten should encounter southwesterly shear along with a turn toward the north. Tropical Depression Ten will also begin to weaken as it encounters cooler SST’s of 25°-26°.

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Dangerous Hurricane Irene

Hurricane Irene, the first of the 2011 Atlantic basin. Hurricane Irene is a very large and possibly a very dangerous storm and is forecast to skirt the coastline of the Dominican Republic as a hurricane, then move out into the warmer waters of the Atlantic. The forecasted track is a very complicated one, but there is some consensus within some of the models with most models having it heading toward southern Florida, possibly skirting the coastline of Florida then a trough will begin to help pull it upward and head north. There is the distinct possibility that it may have landfall as far north as North Carolina. As Irene heads further north, the environment will be very favorable for further development and intensification.

The possibility of Irene going into the GOM has pretty much been eliminated now. The Texas ridge has not retrograded and is actually staying firm. Between that ridge will be the trough digging downward the eastern seaboard of the US. Usually, the troughs will have a tendency to hang around, but this season has been different. The troughs have been digging down almost as fast as they leave. This is also the case with Irene. When the trough leaves, it will leave a more zonal flow (which is more west to east, versus a meridional flow which is more like a roller coaster and is more north to south). The Atlantic (sometimes called the Bermuda) high pressure ridge will be to the right of the trough. Once the trough leaves, there is a weakness and the Atlantic ridge will start to fill in that weakness with high pressure.

Meridional Flow


Zonal Flow

Irene is now heading WNW toward the Dominican Republic and if the trend continues, Irene will be skirting the northern coastline of the Dominican Republic. Irene is forecast to stay on the WNW track for the next 36-48 hours. Irene may lose some strength even though the center will be over water but because of the flow from the south with the high mountains it may temporarily disrupt it enough to lose some of it’s strength. Once Irene is further away from the coastline, Irene is forecast to strengthen rapidly.
The trough will eventually dig down and it will want to pull Irene upward. Irene will then be forced to head NNW and possibly north and will be headed into the southern Bahamas and later on toward the coast of Florida. Timing will be critical as if the turn to the north is much later than the forecast, Southern Florida, including Miami and Fort Lauderdale may be severely impacted. If the turn is to the north happens as forecasted, Irene may just skirt the coastline of Southern Florida with either category one force winds or possibly even just tropical force winds. If Irene just skirts the coast, there will be plenty enough oceanic heat to draw upon and Irene may become a very dangerous storm as it heads north. If the model forecast pans out and misses Florida, Georgia, and the Carolina’s, with little shear, and very warm waters, the environment will be conducive for a very large and strong hurricane with the possibility of winds in the category three or more along the US coastline.

12z GFS Model

12z ECMWF Model

12z Canadian Model

ALL interests from the Dominican Republic, Bahamas, and the US eastern coastline need to watch this storm CAREFULLY. Any slight deviation of the forecast track toward the west can have major implications down the line. And of course, always check for all the latest from the National Hurricane Center site for all official information.

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Invest 93L & Large Tropical Wave

Invest 93L, the resilient tropical wave in the Caribbean, continue its westward motion it’s journey though the “Graveyard” where many storms either weaken or die. The trade winds in that area usually are much faster and especially weak storms are not able to develop roughly between 65°W to 75°W. Once again during the day today, 93L seemed to be developing somewhat albeit very slowly. From the CIMSS maps, there is an increase in the low level convergence (is where the flow over some area is moving inward toward that area) and there is also a marked increase of divergence (where the air at some particular level in the atmosphere over some area is moving outward or away from the area, on average). 93L also has a classic upper level anticyclonic high over it. During the latter portion of the day, 93L began to exhibit signs of cyclonic turning although very, very slowly – mostly in the mid to upper levels but there is no indication of low-level circulation.

Looking ahead, 93L will be dealing with dry air from the west. This will keep any development to a minimum for the next 24-36 hours or so. Shear in minimal so if 93L could get just get a low level circulation, conditions will be conducive for gradual development.

Tracking for 93L is pretty straight forward. Most models forecast that 93L will continue the westward motion toward Nicaragua/Honduras. If 93L were to develop into a very strong hurricane (which is not indicated), then a more poleward shift would result with a turn toward Belize. At this moment, model intensity keeps 93L below hurricane status or just minimal category one.


A large tropical wave southwest of the Cape Verde Islands is the next possible concern. Although it is surrounded by massive amounts of dust (SAL), as it gets closer to 55°W, two of the major models (GFS and ECMWF respectively) have it as a possible major hurricane north of the Leeward Islands with a very possible threat to Florida and also the Eastern seaboard. The ECMWF has been flipping during a few runs so we will have to see how things pan out in a few days. Just remember, these are LONG term models. It’s still way too early to panic but all those in affected areas should keep an eye on this system as it heads westward. If you have not begun to stock up of your hurricane supplies, now would be a great time to do so. The MJO for the next three weeks or so will be in a upward motion for the entire Atlantic basin. Upward motion has a tendency to allow for thunderstorm development. This is the time of year where development ramps up and the Atlantic basin is more active with tropical cyclones.

GFS RUNS

ECMWF RUNS

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Invest 93L (Pouch 15L)

Invest 93L which had been deactivated has been reactivated as of early this morning. At the moment, the satellite presentation of 93L is showing very good convection but this may be due to several factors. One one be that 93L is starting to get into warmer SST’s and also the diurnal maximum. Also, 93L is near the periphery of the Atlantic high pressure ridge. With the trade winds that have been zipping across the Atlantic now being slowed down – the convection is being allowed as the warm air has to rise up.
Convection may wane until 93L is into the much warmer SST’s and increase development of the 93L may not begin until it is closer to 70°W due to dry air to the west of 93L. At this point 93L still has no LLC but possibly might have a mid-level circulation. There is no model support for 93L, but as it heads further west the models should start to pick it up.


Once 93L enters the western Caribbean, conditions for favorable development may be enhanced by the Madden-Julian Oscillation. The MJO upward motion (a wet phase) enhances thunderstorm development.

Green contours indicates upward motion

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Tropical Trains – 92L, 93L, TD Seven, Post-Tropical Storm Franklin

The tropics have finally begun to really fire up as of yesterday. We have old Invest 92L still in the Atlantic. What was Invest 94L was upgraded to Tropical Depression Seven. Invest 95L became Tropical Storm Franklin but as of last night it became Post Tropical Storm Franklin. Last but not least, Invest 93L – but as of 4:30 this morning, 93L was deactivated.

Of the three systems, Post-Tropical Storm Franklin, Tropical Depression Seven, and Invest 92L – all are or will be heading out to sea. Only Tropical Depression Seven has a chance to affect Bermuda as Tropical Depression Seven as it may strengthen and gain Tropical Storm status, and be a threat with tropical storm winds/rain. Since none of the three systems are a major threat, I will just post the image of them along with 93L.

UPDATE: As of the 2pm advisory, Tropical Depression Seven has been upgraded to Tropical Storm Gert.

Although Invest 93L was deactivated, the NHC will probably reactive 93L once it get closer to latitude 55°W – 60°W. Convection has increased slightly and cyclonic turning is present but does not have a defined closed surface circulation. As 93L gets into the Caribbean, the Sea Surface Temperatures (SST’s) will be increasing along with a lot of latent heat energy. As 93L heads further west the Tropical Cyclone Heat Potential (TCHP) will be increasing, this will allow possible heat energy transfer for further system deepening. Shear is present from the north but this will be decreasing but dry air may inhibit some development.

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The long term track for 93L is very uncertain. A slight shift in the pattern may develop where the Texas high pressure ridge may be forced to head westward. The Atlantic high pressure ridge may be rebuilding once Franklin, TD7, and 92L have curved out to sea. This should leave a weakness between the two ridges. A more zonal flow is forecast develop somewhere in the mid – western Canada. This should keep 93L on a more West or WNW track for a few days. Where that weakness between those ridges is going to steer 93L. If 93L develops as a weak storm, a possible track will be for the continued W – WNW toward the Yucatan where as a much stronger and deeper storm would tend to turn 93L NW. Being that 93L doesn’t have a closed surface circulation, it is too difficult to determine where 93L will go or even if it develops into a tropical cyclone. So at the moment there is no immediate concern but those in the Caribbean, and the southern US should keep an a close eye in 93L.

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Invest 92L (Pouch 14L) , Invest 93L (Pouch 15L)

It seems that that Cape Verde season has begun in the Eastern Atlantic.
Two Invests, 92L and 93L have been tagged and designated.
92L had been designated on 8/7 but the next day it was deactivated only to be activated again on 8/9. 93L on the other hand has just been activated late yesterday. This is the time of the year where most of the tropical waves come off the edge of Africa and possibly develop into tropical cyclones.

Invest 92L
Invest 92L is a no longer a well defined low pressure system. Instead it now is negatively tilted system that looks very ragged. Although there is dry air entrained into the system, 92L may become at least a tropical depression once the system begins to create a lot more convection within the center, assuming it survives. This may take a few days due to the SAL or dry air that is wrapping around the system from the NW and W of the center, thus inhibiting development. As 92L gets much further west the SST’s will be increasing allowing further development.

As for the track of 92L, this all depends on some of the timing, but a lot of the models are forecasting a trough that will be over the eastern seaboard which should allow a recurve once it lifts out and sending 92L out to sea. The problems with that is the long term and the models will change. 92L will probably recurve, but how close to the eastern seaboard is still early to predict.

Invest 93L
93L who came off the edge of Africa yesterday afternoon and is a large system but it is somewhat linear and not looking like a well developed system with excellent cyclonic turning. Gradual development of this system is forecast. Because Invest 92L cleared the “path” of the SAL, 93L will not have the problems of dry air entrainment, at least for the next several days.
As 93L tracks WNW, the long term track is uncertain. The long term forecast, assuming that 92L will lift out due to a trough, a more zonal flow will develop somewhat in the area of central to SE Canada. (A zonal flow is more west to east and somewhat straight, whereas a meridional flow has more north and south). This will leave a weakness in the eastern seaboard because of the high pressure ridge that has been over Texas for several weeks now and the high pressure ridge in the Atlantic. Once there is that weakness, the Atlantic ridge will want to “fill that area of weakness”and expand the ridge westward. Depending on how deep the ridge develops will be the steering current for 93L. This weakness may allow 93L to get very close to the eastern seaboard or even have landfall as 93L starts a recurve due to a trough that is forecasted by the long term models. As usual, there is plenty of time for things to change, but all interests should begin to monitor 93L.

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Tropical Storm Emily – A Florida Threat??

Tropical Storm Emily has continued to trek more toward the west than west-northwest and is still a minimal tropical storm. Recon is investigating Emily as we speak and will give a better estimate of the intensity at that time. Although the center seems to be well defined, the center has decoupled from the mid-levels with all the convection well far from the center of circulation. The dry air to the NW of Emily along with some shear from the westerly wind shear has the culprit for Emily. There is also a high south of Emily and the flow from that is also helping to remove some of the convection from the center of Emily. Some convection may try to wrap around the center again, whether or not it can sustain it is difficult to say. EDIT The convection has started to wrap around the center of Emily and the “naked swirl” is no longer shown in the latest images.

As I alluded to in my previous post, Emily is expected to make a turn to the northwest as it approaches either the western end of the Dominican Republic or Haiti. One of the problems right now is that the trough that was to pick up Emily is beginning to lift out and Emily has still been on that westward track. The forecast was for Emily to picked up by that trough. There is the possibility that since the trough is lifting out and Emily is a weak storm, Emily may not be picked up by that trough. Why Emily has not turned northwest as of yet is because there is a high pressure ridge in the Atlantic and another high pressure ridge in the midwest heading east. Emily being too far south and also being a weak storm, the two different ridges may have somewhat shielded the trough from picking Emily up. A shortwave trough in the southeast US is forecast to head southeast and this is expected to then pick up Emily and this will make a sharp turn taking Emily to the northeast. The problem is if Emily misses the first trough then Florida may be in Emily’s sight.

Now assuming that survives the trip over Hispaniola, Emily should regenerate and slowly strengthen. The high pressure ridge from the midwest will bring both subsidence and dry air off the coastline of the Southeast. This will make the strengthening gradual. Although there is no real consensus within the intensity models, some have Emily near a high category two where as others have it below hurricane strength. The intensity models that have it over hurricane strength I think have to be discounted unless Emily survives the crossing over Hispaniola in somewhat intact.

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