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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Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
Now - let me read back a bit and try to figure out this morning's scenarios.
Yeah, it was okay. I didn't really celebrate it, a lot going on. There's a time and a place.
Be better if the Ravens win tonight. :)
So far the TROF remains flat above 30N:
so other than that what? you saying he slows but doesnt turn?? continues West/Westnorth west?
But I'm not staying up to see it reach 50w, I'll be back in 4hours to see how that went, but one thing is for sure, this thing isn't slowing down at all.
PREVIOUS FORECAST TRACK. IGOR IS EXPECTED TO TURN WEST-
NORTHWESTWARD IN ABOUT 24 HOURS AND THEN NORTHWESTWARD IN A
COUPLE OF DAYS AS IT APPROACHES A BROAD TROUGH OVER THE CENTRAL AND
WESTERN ATLANTIC.".....
from the latest discussion from the NHC.
Ridging/high pressure over the SE US and western Atlantic still in place to limit western movement at some point.
HURRICANE IGOR DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010
500 AM AST MON SEP 13 2010
...THE HURRICANE CONTINUES TO MOVE WESTWARD AT 11 KT...AND IS ON THE
PREVIOUS FORECAST TRACK. IGOR IS EXPECTED TO TURN WEST-
NORTHWESTWARD IN ABOUT 24 HOURS AND THEN NORTHWESTWARD IN A
COUPLE OF DAYS AS IT APPROACHES A BROAD TROUGH OVER THE CENTRAL AND
WESTERN ATLANTIC. ALTHOUGH MOST OF THE GLOBAL MODELS SHOW THE
TROUGH FLATTENING IN 3 TO 4 DAYS...THERE ARE DISAGREEMENTS IN HOW
MUCH...IF ANY...SUBTROPICAL RIDGING BUILDS IN THE WAKE OF THE
TROUGH. THE ECMWF AND UKMET MODELS CONTINUE TO BUILD MORE RIDGING
NORTH OF IGOR...RESULTING IN A TRACK FARTHER WEST THAN THE OTHER
MODELS. OVERALL...THE MODEL GUIDANCE HAS SHIFTED SLIGHTLY TO THE
RIGHT FROM THE LAST CYCLE AND THE OFFICIAL FORECAST IS NUDGED IN
THAT DIRECTION...BUT REMAINS ON THE SOUTH SIDE OF THE GUIDANCE
ENVELOPE...
At the lower levels it's over 25N
That is a tricky statement as they don't specify the heading, west can have a hint of north to it and still be west.
Link
With the tail end of the first trough moving up under the second trough, is Igor pushing his way west?
LOL....never!!!
Thanks StormW sir.
I forget to look at the Dvorak. You can clearly see what should turn him, "if the trough persists".
Oh, and how does a trough flatten out? Is it the same as filling in?
Rainbow
TFP's are available.
Hard to say, Storm. I guess I interpret the broad or flat trough as a zonal jet stream rather far south that will persist for several days. Prohibiting ridge building. The NW periphery of the mid-Atlantic ridge under constant attack. Not a huge thing-a subtle and constant thing.
If high pressure over the SE (to the west of Igor) stays strong, the weakness remains and Igor has to go N-ish in between the ridges.
A slow creep into the strong westerly flow. In general, I think the track models are in good shape.
But I do remember Earl!
Igor
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)
Dymamic Models (More sophisticated models)
I know!!!
As always Storm, yours are the comments my wife and I look for. Please excuse me if I'm asking a question that's already been answered, but what do you think will happen if Igot passes 50W and doesn't show any signs of a northward tug?
Thanks in advace, and have a great day!
Just asking this, because so far this year the models and particulary the NHC have been pretty good.
Yes. :0
Not Funny at all.. It needs to point to NYC
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