92L still a threat to develop; Igor a hurricane; TD 12 forming near Africa
Tropical disturbance (92L) over the Central Caribbean, a few hundred miles south of the Dominican Republic, remains a threat to develop into a tropical depression. Satellite loops this morning show 92L may be starting to form a surface circulation, and an Air Force Hurricane Hunter aircraft will investigate 92L this afternoon to see if a tropical depression is forming.
The storm has only a modest area of heavy thunderstorm with limited low-level spiral banding and upper-level outflow, thanks to an infusion of dry air last night that disrupted the storm. Long range radar out of Puerto Rico shows that heavy rains are affecting that island, but there is no rotation to the radar echoes evident. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are hot, 29.5°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air could interfere with development at times over the next few days.
Figure 1. Morning satellite image of 92L.
Track forecast for 92L
The disturbance is moving west to west-northwest at 15 mph, and steering currents favor a continuation of this motion for the next three days. Model support for development is scattered. The GFS and NOGAPS models do not develop 92L. The GFDL and ECMWF models predict development, with a track taking 92L into Belize or Mexico's Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches today through Monday morning; southern Haiti can expect similar rains tonight through Monday night, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba can expect rains in the 2 - 4 inch range. Once 92L crosses the Yucatan, the ridge of high pressure steering it is expected to remain in place, forcing 92L to a second landfall in Mexico south of the Texas border.
Intensity forecast for 92L
NHC is putting the odds of 92L developing into a tropical depression by Tuesday at 50%; I'd put them higher, at 70%. However, time is running out for 92L to become a hurricane before hitting the Yucatan Peninsula on Wednesday. Given the current disorganized state of 92L, it would be difficult for it to intensify quickly enough to become a hurricane by then. The storm may also suffer another of its mysterious evening collapses, where it loses most of its heavy thunderstorm activity. However, the SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and water temperatures are certainly warm enough to support development. The main detriment to intensification is likely to be dry air, and 92L could wrap in some of the dry air to its northwest at times, slowing down development. There are a number of research flights being made into 92L this afternoon that should help long-term efforts to make better predictions in the future on whether or not disturbances like this will develop or not.
Figure 2. Morning satellite image of Igor.
Igor
Hurricane Igor appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is low, 5 - 10 knots, and is expected to drop below 5 knots for the next five days. Waters are warm, 28°C, and will warm to 29°C by Wednesday. Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor is undergoing a period of rapid intensification today, and will probably be a Category 3 or 4 hurricane by Monday.
The track forecast for Igor remains unchanged. Igor will move west under the influence of a strong ridge of high pressure for the next 2 - 3 days, then turn more to the west-northwest then northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor may be a threat to Bermuda, and does have a small chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 15% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 10% for Canada. The forecast steering pattern for the period 5 - 12 days from now from the ECMWF and GFS models shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. Recent runs of the ECMWF model indicate that these troughs may not be as intense as previously thought, so it is possible Igor has a higher chance than usual to hit land than climatology suggests. One wild card may be the possible development of TD 12 behind Igor. If TD 12 develops into a hurricane, and moves close to Igor, as some of the models are suggesting, the two hurricanes could rotate around a common center, forcing Igor more towards the coast of the U.S. The long term fate of Igor is difficult to predict at this point.
Tropical Depression Twelve forms
Tropical Depression Twelve formed between the Cape Verdes Islands and coast of Africa this morning, and is already affecting the Cape Verdes with winds near tropical storm strength; sustained winds of 35 mph were recorded in the northwest Cape Verdes this morning. You can follow the progress of TD 12 through the Cape Verdes today using our wundermap.
Next post
I'll have a new post Monday morning, and perhaps late this afternoon if events warrant.
Jeff Masters
Reader Comments
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I think MIAhurr09's comment about explosive deepening is what our friend wanted to emphasize. I admit I kinda took it that way, and didn't assume he meant a literal sub-800mb storm was possible.... but here is a "teachable moment" for those relatively new to TC formation and deepening....
Wilma obviously qualifies, however, Earl did not.
The most recent storm to exhibit such rapid strengthening was Ike in 08'.
Agreed.
Thanks for being polite about it.
92L looks like it's opening up into a Tropical Wave, by the way it's elongated...
And Hurricane Igor continues to go through explosive deepening. I believe that Igor is a major hurricane, it this time, at the rate that it's stregnthening. It also has a very good shot at becoming a Category 5 hurricane.
Igor is beginning to demonstrate properties of an annular hurricane, although it is still unclear if it will eventually, or not.
We also have a new Tropical Depression! This is likely to become Julia, and intensify into the 5th hurricane of the season. Lots of stuff to watch, right here in the busy Tropical North Atlantic. The African Wave Train, continues at full speed...
A Low is forecast to form on the stationary front in the next 24 hours at 35N 57W. That will pick up Igor for sure.
http://www.opc.ncep.noaa.gov/A_sfc_full_ocean.jpg
SUNDAY 9:30 AM
SUNDAY MORNING COMMENTS
First, on Igor. True to the ideas yesterday, the European has shifted west and now has Igor reaching as far west as 72 west. This is over 12 degrees from the 00z run,sep 10th. The UKMET remains west and I have not seen the 00z Japanese out that far. The GFS remains insistent on its recurve east of 65 west.
There is probably a simple rule to use here. If the storm is south
of 25 north at 70 west, the US coast will most likely have at least tropical storm impact from this. The fact is the the models are trying to get the storm to hook with the atlantic trough, and since the pattern is in a retrogressive mode, that trough keeps dipping in further west with time until by the time we are out to 168 hours, if the hurricane is south of 30 north, there really wont be anything to get it out of there. This is why you see the Ensembles, and again the Euro leads the way with predicting this, showing such a spread out area of low pressure once to day 8.. from the bahamas to south of Newfoundland. because some of its members take it westward. In many ways, the combination of Igor, what will be Julia now off the African coast, and the developing cyclone in the Caribbean supply us with a similar case to Earl, Fiona and Hermine... if one looks at Igor as the threat to the east coast, Julia having to recurve if Igor comes as far west as I think it will ( to at least 70 west) and what will be Karl the threat to Texas in the longer term via the Yucatan and then a fade northwest at the end. In fact one might as well correct the Euro north ( its track is into Tampico but at least it sees it, the GFS would have you believe nothing is there) since a) its ensembles are leaning north and b) its not like nothing has been aimed there so far.. it would make the 4th classified system to make a landfall within 75 miles of Brownsville, ALex, Hermine and the depression being the other 3.
Speaking of the system in the Caribbean, now it has a chance to go as the convection that has fired is much more co-ordinated with the low level wave. Yesterdays impressive look was all outflow but the low level wave was well behind what looked to be the mid level center and then upper outflow. Not so today as a center near 15.5 and 69 looks to be coordinated with the cloud shots and the data.
This ship report:
SHIP S 1200 16.90 -69.20 149 318 50 24.1 - 13.1
near 17 north and 69.2 west has a northeast wind at 24 kts with 13 foot seas and a pressure at 1009 mb Looking around it, I see a sharp windshift in that area with a southwest northeast trough, and its co-ordinated nicely now with the cloud shot, so this should start going now. If I had a hatch-it job, now I would have it as a high threat for development with in 48 hours. Of course, I dont have a hatch-it jobs as I am not allowed to play with sharp objects.
By the way, 13 foot seas area the give away that something is cooking. You dont get a 13 foot sea without strong concentrated winds in the tropics.
In looking at Igor we find again the US models have been too far north too quick. Its on the order of 150 miles in 3 days.. and that is not bad.. in fact its a good forecast overall but the same error continuing would mean that the model would try to recurve the system. The first challenge is tomorrow and Tuesday so lets see where it goes. Looking at the Euro hurricane forecast, there are more members south of its track than north. And as I have stated several times already this is going to be the strongest hurricane of the season thus far, hence the big threat if it comes as far west as I have it.
By the way, when you see a trough off the east coast in 192 hours, that is because the model forecasting it is recurving the hurricane. Its not because there is a trough there by then, its the hurricane that causes the
trough. If there is no hurricane, or its stalled next Sunday between Hatteras and the Bahamas, then the whole map is different. My point is that if you look at the runs that dont recurve the storm, then you get a different map. There is no trough off the east coast, without a recurved storm next week, as the pattern is shifting. In fact a look at the Euro shows it has another development trying to start up day 10 near Puerto Rico anyway,and of course the GFS day 15 is trying to scare the daylights out of the gulf with its monster. The point being this pattern is ripe for storms and rumors of storms
One more thing.. a word about my overall seasonal power index to replace the ace.. using pressures of each storm set against 1000 mb as the 0 point. If we look at the storms this year.. Alex at 947 would get 53 points, Bonnie and Colin 0 ( pressures stayed above 1000 mb) Danielle at 942 would have gotten 58 points, Earl at 929 71 points, Fiona at 989 11 points, Gaston none, Hermine 990 mb 10 points and so far Igor at 980 with 20 , you come up with a much better scale for how strong the season is. I think Igor is getting to 920-930 btw. But I am willing to bet when we get done with this season, if we total the pressures of these storms up against previous known seasons, this is a top 5 season. You watch.
BTW some wild weather coming the next two weeks as heat refires and tries to come northeast into a stubborn boundary, but summer is not done yet for some of you that are a bit on the chilly side now. Interestingly enough, the same old GFS nonsense with temps has been going on from when I was in college the US models overcooling the east. For all the cold air that was coming, the days of 6-9 below normal over the east coast, where the heck is it. PHL last 5 days plus 1.4 Bos plus 2.4..even Chicago, where it was supposed to have gotten quite chilly is only 2-6 below normal the past 5 days. Heck this surge coming this weekend or next week gets up into there, it will wipe out 10 days of cool with 2 days of warm
But there is no question that cooler air has gotten into the pattern since Aug 22, when we named Danielle. And since by Sept 22 we may be all the way to the letter L or M, I think I have made my point to you about what sets seasons off. In fact the only thing I need now ( besides running the total numbers up a bit more) is to get the end game to give me the impact scores I need to verify. Again faced with the problem of having to balance the desire to be right.. and by doing so, performing a valuable service, against the implications of such things. It is a problem I wrestle with constantly
thanks for reading, ciao for now
12Z CMC...
there will be lots to learn and great data to review.
With all due respect, Ike qualified for "Explosive" Intensification as well. The National Weather Service describes rapid deepening as a decrease of 42 mb's in a 24 hour period. However, Ike dropped 44 mb's in 12 hours, which is well within the range of 2.5 mb per hour for 12 hours for Explosive Intensification, as defined by the NHC.
Perhaps..
Link
EDIT: you edited your post, nvm
Good Summary.
Tropical Tidbit for Sunday, September 12th, with Video
988mb at 5 AM AST & 952 mb at 1130AM AST= 36 mb drop in pressure or a drop of 5.54mbs/hr!!!
I know, I fixed it as soon as I posted it.
Thanks for the clarification though.
Thank you.
Knew it did.
God on high, i'm not saying it will not recurve, i'm just skeptical. I believe StormW is not predicting a full recurvature either, same with Joe Bastardi. Sorry, but some models do NOT recurve Igor. Depends how flat the trough may be.
Nice way of putting it....
heheheh
:D Hi Levi!
Earl dropped 22 mb's in 12 hours, and 37 mb's in 24 hours. That qualifies for RI, but not ED, as defined by the NHC. Earl's fastest rate of intensification was -1.83 mb/hr for 12 hours, or -2 mb/hr for 6 hours.
If the high that is protecting the TX/LA coast right now bridges with the other, will that move the high off the TX/LA coast?
Its unofficial though.
Wait, but to get 2.5mb an hour for 12 hours you only have to drop 30mb, 42mb would be 3.5mb an hour. I mean if the NWS said that then ok but they kinda contradicted themselves.
Could lead to a FLDewey joke.
Oops... You mean Igor? :D
Still have to wait till it gets into the Western Caribbean where conditions may be a bit more favorable for development.
Pretty much guarantee that this isn't at 105mph.
Two different definitions Hurricane Swirl. NWS describes Rapid Intensification as 42 mb's in 24 hours. (Loosely)
NHC describes Explosive Deepening (an even stronger rate of intensification than RI) as 2.5 mb/hr for 12 hours or 5 mb/hr for 6 hours.
Rule #1..ALWAYS be PREPARED...
Since the pattern change where the sub tropical High broke down over Central Russia on 8-20-2010, in 23 days we have had Danielle, Earl, Fiona, Gaston, Igor an the next "J" storm is brewing..that is SIX storms..wow!!
Link
Puts 92L onshore near Corpus Christi next weekend. (caution: 7 day track and intensity errors can be infinite)
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