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October 2011

Rina weakens significantly, but still a hurricane hit coming for Cancun

   Posted by Levi at 8:46am on October 26, 2011

I woke up to a very different Rina than I went to bed with last night. Recon data from a new plane shows that the pressure has risen to 984mb, and Rina’s winds have backed off to Cat 1 strength, indicating that she has weakened considerably, and her eyewall has collapsed almost entirely. There are only really two possible explanations for this. One is dry air entrainment, and the other is cold water upwelling underneath the slow-moving storm. I am dismissing the former in favor of the latter. TPW products and microwave imagery don’t indicate that dry air penetrated Rina’s core, and she was embedded in a pretty moist environment last night with beautiful outflow aloft. Her problems seem to have been caused from the inside, and she has likely depleted the water beneath her of energy.

The big question on everyone’s minds is likely why we didn’t see this coming. The answer is that we knew it was a possibility with a slow-moving storm, but my idea was that it would not be a significant problem for Rina, based on a comparison with Wilma. Wilma was moving just about as slow as Rina at her peak, and through the same area of the Caribbean over similar ocean heat content. However, despite being the strongest hurricane on record, Wilma did not suffer from this upwelling problem. Logic seemed to dictate that Rina, being weaker and moving at a similar speed, would not suffer from it either. My guess is that I was wrong about that.

The northeastern Yucatan is getting off extremely fortunate now, as Rina will not be a major hurricane brushing through the Cancun area. However, she is not falling apart completely, and is beginning to move faster over warmer waters again. She will likely still be a hurricane delivering a hit to the region, perhaps even restrengthening slightly, but not nearly as strong as she would have been. Folks should still be prepared for a bad storm in the Cancun area.

This also changes the end-game track for Cuba and Florida. In some ways it seems like some of the global models saw this coming, though it’s hard to tell since Rina was not being resolved properly on some of the models. As a weaker Rina approaches the Gulf of Mexico, she will be more susceptible to dry air and wind shear, and should weaken quickly to a tropical storm. The resulting intensity and track should be fairly similar to Hurricane Paula from last year. The forecast from yesterday was based on Rina being a cross between Paula and Wilma, but with the recent weakenig, it will be much closer to a Paula-type situation. Rina may not make it to south Florida if she is very weak coming away from the Yucatan, and may actually follow yesterday’s NHC track closely. Had she been as strong as she was forecasted to be coming into Cancun, she likely would have tracked farther north. A weaker system, however, will be more likely to be pushed on by the front over the north gulf coast in 3-4 days, and get somewhat trapped near Cuba and the Florida Straights. While some weather may still affect Florida, it likely won’t be more than a blustery weekend, not quite as blustery as it would have been.

We shall see what happens!

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Rina likely to become a major hurricane and take a swipe at Cancun, then S. Florida

   Posted by Levi at 1:40pm on October 25, 2011

Hurricane Rina has strengthened markedly since yesterday, and is now a Category 2 with a central pressure of 972mb. The pressure fall has slowed during the last several hours as the eyewall has had some issues closing off on the eastern side, but gradual strengthening should continue through tomorrow, as Rina is under a very favorable environment aloft, with outflow expanding in all directions.

The Cancun area of Mexico is due to receive the very worst that Rina has to offer around early Thursday as Rina curves northwest around a mid-level ridge to her northeast. Rina could peak at a strong Cat 3 or even possibly a weak Cat 4 before moving into the Cancun area. She could begin weakening off her peak a tiny bit before landfall, but folks in the northeast Yucatan should be preparing for a hit from a major hurricane.

The track after a swipe at Cancun should have Rina continuing to recurve northeastward, likely making a run at the Florida Keys and extreme south Florida itself. The NHC track as of the 11am update is still following some of the models that stall Rina and force her back southeastward into Cuba and the northwest Caribbean. To me, such a track seems less realistic, given that no model is correctly initializing Rina because of her small size, and with a shortwave vorticity maximum racing along I-20 during that time frame, it seems unlikely that Rina will be blocked from an ENE escape. The video goes over this using the GFS. The GFS and HWRF 12z runs show the track that I like right now.

Rina will be weakening as she comes off of the Yucatan towards Florida due to a strengthening jetstream to the north which will be shearing her, and Rina is unlikely to hit Florida as a strong hurricane. A strong tropical storm or a weak Cat 1 at worst is more likely to be what Florida has to deal with, which is better than it could have been. Mexico will be the hardest hit by this storm.

Elsewhere, Invest 97L in the eastern Caribbean may have to be watched once it gets to Jamaica’s longitude. If it finds a sweet spot south of Rina, we may have another tropical depression to deal with, but we still have a few days before 97L will be an immediate threat.

We shall see what happens!

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Rina forms – could be a problem for the Yucatan

   Posted by Levi at 4:41pm on October 24, 2011

Tropical Storm Rina has formed in the western Caribbean Sea, the 17th storm of this active season. Convection has been firing strongly since yesterday afternoon, and the previously exposed center is now tucked under the southeast quadrant of the CDO. The daytime today will be a big test to see whether Rina can sustain this level of convection in the face of very dry air to her northwest which is trying to get entrained into her circulation. However, upper-level conditions are improving, and Rina is now moving over progressively higher levels of ocean heat content, which should help fuel gradual intensification over the next few days. A category 1 hurricane at least is looking more likely now that Rina has put on a good show, though how much she has really strengthened is yet to be determined by the next recon plane. With 3-4 days over water ahead of her, Rina could easily become a strong Cat 1 or weak Cat 2 before interacting with the Yucatan Peninsula.

Rina is stuck in weak steering currents, but some general guiding influences will shape her track. Broad troughing over the southeast U.S. is being replaced by ridging during the next 48 hours, which should curve Rina westward towards the Yucatan. With pressures very high over Central America, the models showing Rina diving WSW into the continent look unrealistic, especially since she is a stronger system than they forecast, which should help keep her north. In 4-5 days, a new trough is forecasted to dig into the southern U.S., which should erode the ridge and allow Rina to resume a northerly motion near the east coast of the Yucatan. This could end up in a nasty swipe for Cancun and surrounding areas. A northeast escape and absorption into the jetstream would then seem likely, with a track near Cuba or southern Florida. However, this is 5 or more days away still, and details are going to be hard to work out until Rina starts to make the turn.

Cuba, Florida, and the Bahamas should watch Rina, as she could be a fairly potent storm coming out of the Caribbean, but conditions will likely deteriorate quickly north of about 22N, as the jetstream will be screaming directly across the Gulf of Mexico, imposing shear on any system trying to leave the Caribbean waters. Thus, weakening is expected after Rina recurves northeastward. There are still a lot of uncertainties in a track this slow and fragile, but the Yucatan from Belize to Cancun should keep a close eye on what could become Hurricane Rina eventually if she survives today and continues to organize.

We shall see what happens!

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Another development threat in the Caribbean

   Posted by Levi at 9:39am on October 21, 2011

Mother nature may not be done with us this season. Despite the MJO leaving the western Atlantic and this time of year usually being when things start quieting down, we have another disturbance in the southwest Caribbean that has a decent shot to develop. Invest 96L is a smaller circulation than the very large 95L, and has a better chance to wind up in a consolidated fashion that could easily get named. This system is in weak steering currents and will be slow to move around during the next few days, but should slowly drift north or northwest due to high pressure over the eastern Pacific and central America while a trough sits over the eastern U.S. for the next 48-72 hours. After that, the flow over the SE US becomes flatter and could steer 96L slightly to the west for a time, but a 2nd trough quickly dives into the eastern U.S. in 5-6 days that would easily recurve anything sitting in the NW Caribbean. For this reason, Florida, Cuba, and the Bahamas should be on the lookout for any trouble to their south, as it could come their way. Central America should be wary of 96L as well. The ECMWF, GFS, UKMET, and CMC are all becoming more aggressive on development now in recent runs, with the ECMWF and GFS coming onboard with significant development for the first time in last night’s runs.

Another area of low pressure east of Trinidad may propagate into the Caribbean next week that could be a potential development threat behind 96L, or the two systems may interact with each other, so we may have a fair amount of things to watch this weekend and next week.

We shall see what happens!

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Invest 95L may get named – could be close to the last system of the season

   Posted by Levi at 5:05pm on October 17, 2011

Thanks for all of the birthday wishes yesterday!

Invest 95L is now centered just north of the Yucatan, and remains a broad and elongated area of low pressure. A large lobe remains over the Yucatan, with another lobe of vorticity located near the convective activity which is all off to the northeast of the Yucatan Channel. The system is getting sheared from the west, and the circulation needs to tighten before it can be classified as a tropical storm. The NHC has had to up their chances for development to “high”, and we may yet get this named Rina before it gets absorbed into a front within 48 hours. This front will drag 95L northeastwards in the general direction of northern Florida, though the worst weather associated with this system will be affecting all of the Florida Peninsula ahead of the center’s arrival. Again, Florida will be experiencing tropical storm conditions regardless of whether the invest is named. TS-force winds are already being observed in the Florida Straights and the Yucatan Channel. Wind shear won’t allow 95L to strengthen much beyond moderate tropical storm strength if it does get named, and heavy rain will be the main story with this system. It will be deepening baroclinically as it moves up the eastern seaboard and becomes part of a monster extratropical low over New England later this week.

Looking ahead, 95L may be one of the last significant systems of the season. The MJO will still be around for a little while and the Caribbean is much warmer than normal, so there is still a chance for the Caribbean to spawn some low pressure areas even through November, but if we don’t get anything by Halloween, then the season will be pretty close to over. Caribbean folks always have to be on the lookout until December, but don’t expect a whole lot of activity from here on out. It’s been a deadly year, but I think we got off lucky again overall. Irene was the only truly bad storm this season.

We shall see what happens!

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Watching trouble in the Caribbean – heavy rainfall is the big story

   Posted by Levi at 10:03am on October 15, 2011

We are still watching an area of broad low pressure in the western Caribbean, generating a large area of moderate-deep convection this morning. Prolonged rainfall is likely causing flooding problems for central America due to this monsoonal depression sitting over them for so long, and they will have to deal with it for a couple of days longer yet. The main center is near the coast of Belize and will be drifting northward or NNW over the next 2-3 days hugging the Yucatan, but we will have to watch the low pressure extension east of it for any kind of secondary low development. A tropical wave racing in from the east has decided to come and play, and may introduce an interesting new element to the situation by enhancing vorticity over the water.

Whether we will get a classified system remains to be seen, though I still feel we have a decent medium chance to get a tropical depression or tropical storm. Any system that does form may not have ample opportunity to get very strong, but either way Florida will be in for a very heavy tropical rain event as a front dives down from the northwest and drags whatever is sitting in the Caribbean northeastward. The GFS and the other models except for the ECMWF still seem too far west with the low, and drying out the western Caribbean entirely in 48 hours seems unrealistic given how warm the water is and how the MJO is buried in phase 1. I like the Euro’s idea of a northward drift and then a northeast escape, which agrees with what my ideas have been on the situation thus far. We will have to closely monitor the situation for the next 3-5 days.

We shall see what happens!

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Western Caribbean bubbling for a few days; heavy rain for Florida next week

   Posted by Levi at 9:18am on October 14, 2011

As advertised, the western Caribbean is becoming much wetter as thunderstorm activity increases over the region east of the Yucatan Peninsula. A broad monsoonal low is rotating over the region with one center over central America and another east of Nicaragua. This latter one may start rotating up to the northwest and could aid in consolidating the area into a tighter low east of the Yucatan this weekend. Given the large nature of the system and land interaction, development will be slow to occur, but with several days to work with before it has to move anywhere, it should be watched carefully.

A trough coming down in 4-5 days over the central-eastern U.S. will be drawing anything sitting near the Yucatan northeastward in the general direction of Florida, making at the very least a heavy tropical rainfall event in the works for them next week. The map I put out yesterday shows a medium-high chance for development in the western Caribbean over the next few days, with an eventual escape northeastward. It should be noted that given the large nature of the system, it may not even have a chance to get very strong at all before being picked up by the trough, but it has enough time to be a cause for concern. Residents in the NW Caribbean and Florida should keep a close eye on the situation.

Half of the models led by the GFS take the low westward into the Bay of Campeche before the trough tries to pick it up, a movement that is not impossible but that seems less likely to me given the aggressive eastward progression of the MJO and the warm water in the Caribbean. A meandering movement with a slow drift northward this weekend and then a quicker northeast escape next week seems most likely to me right now. The ECMWF and UKMET currently support this solution.

We shall see what happens!

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Watching for Caribbean development this weekend and next week; heavy rain for C.A.

   Posted by Levi at 9:20am on October 12, 2011

The Atlantic is fairly quiet today. Most of the tropical action is out in the eastern Pacific where Jova just moved ashore and TD 12 just formed, but is also about to move inland. TD 12 is the main carrier of the monsoon circulation right now, and thus it will be a feature to watch over the coming days. The models have it meandering around but not really wanting to leave central America for the foreseeable future. The GFS and ECMWF have backed off a bit on development in the Caribbean, in favor of keeping low pressure tangled up with central America. While this may happen and cause a longer delay before an opportunity for development, the western Caribbean should still be monitored for possible migration of low pressure into the region this weekend and next week. Either way, central America is likely to receive copious amounts of rain over the next week or so as the monsoon circulation sits directly over them, and flooding could become an issue for those countries.

We shall see what happens!

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93L inland but not named; Jova aiming for Mexico; Caribbean is next for trouble

   Posted by Levi at 9:03am on October 10, 2011

Invest 93L is now inland over the northern Florida peninsula and will continue northwest into the panhandle today. One of the great mysteries in my young career will be why this system was not named Subtropical Storm Rina last night. The NHC’s own words to describe 93L last night as Florida received hurricane-force wind gusts were “A NON-TROPICAL GALE CENTER.” That’s hard enough to justify over 29C water anyway, but AMSU showed a clear warm-core structure on all of its passes of 93L, and a tight 999mb low with a buoy off Cape Canaveral showing exponential drop in pressure and increase in winds as the center came near is a signature that is only seen in tropical cyclones. In my mind there is no way to excuse the goof-up that happened last night. Hopefully someone does something about it in the post-season. Florida knows what they got hit with last night.

Hurricane Jova is moving northeastward towards Mexico with a clearing eye and will likely be a major hurricane at landfall. Our thoughts and prayers go out to the people there. Jova moving eastward illustrates how the entire monsoon circulation is shifting eastward as the MJO aggressively progresses into phase 8. One of the strongest bursts into octant 1 that we have seen in quite a while will be occurring over the next 10 days, and the Caribbean may get a shot at development within the monsoon circulation cell next week. The ECMWF shows low pressure east of the Yucatan in 7 days, and the GFS has been inconsistent with the timing, but shows development eventually as well. While the trough will be vanishing from the eastern U.S. in a week’s time, it will be short-lived, as by day 10 all of the ensembles have a big trough returning to the east, indicating that any trouble brewing in the Caribbean may have an opportunity to come northeastward towards Cuba, the Bahamas, or Florida.

We shall see what happens!


The southeast U.S. to get a subtropical soaking; Bigger problems may arise by mid-month

   Posted by Levi at 8:29am on October 7, 2011

Thunderstorm activity is on the increase near and east of Florida as an upper trough digs into the eastern Gulf of Mexico. This is the catalyst that we talked about yesterday that would be needed to spark stormy weather that could lead to subtropical development early next week. The air is still very dry in this area, and won’t magically become a sauna, but gradually these thunderstorms will throw enough moisture into the air that some feedback should be able to occur and consolidate into an area of low pressure just east of Florida. The ECMWF and CMC are still hanging on tight to their idea of the low forming in the eastern Gulf of Mexico, but I continue to favor the GFS solution for being farther east, to the east of the trough axis where the dynamics are more favorable. Even if we get weak low pressure to stack with the upper trough in the Gulf of Mexico initially, a secondary low should form to the east and become dominant as it phases northward into the southeastern states. Even farther up the eastern seaboard may see some interesting weather if the system waits long enough so that it can phase with the trough coming out of the plains in 6-7 days.

Overall, several days of very blustery weather with heavy rains, up to several inches, and gale-force winds in places, is in store for Florida and surrounding areas this weekend and into next week. This won’t be anything particularly dangerous, but we might get a named subtropical system out of this mess that makes life interesting for a few days. This development fits perfectly into the pattern that we’ve been discussing, where high pressure builds strongly over the eastern United States while the MJO is shifting back into our area of the world, supporting mischief.

This is far from the last we will hear from the tropics in this pattern though. As I have spoken of, as soon as our subtropical entity gets absorbed into the east coast trough, it shifts east and allows the eastern U.S. to get charged up with high pressure a second time, focusing convergence down in the Caribbean again. With the MJO becoming fully focused in our area of the world as the two eastern Pacific storms move eastward, the monsoonal circulation may have a chance to ignite on the Caribbean side in 8-12 days, allowing a storm of more truly tropical nature to develop and move northward towards the southeastern United States, just as I have been warning about for so long in this pattern. The GFS and ECMWF are both starting to consistently show this 2nd system developing in 8-10 days. I show in the video how the monsoon circulation makes a massive leap eastward during the next week, setting this up.

We shall see what happens!

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