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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Only a slight shift right.
Maybe, maybe not. We'll see, but most hurricanes end up eventually undergoing EWRC's except in rare circumstances. Igor is still an incredibly impressive cyclone, but it has lost a little symmetry during the past couple hours. Could just be a fluctuation however. Looks like the ADT has topped out for now.
OFFICIAL FORECAST STILL LIES ON THE SOUTHERN SIDE OF THE GUIDANCE
ENVELOPE UNTIL IT BECOMES CLEAR THAT IGOR IS READY TO TURN. THIS
SOLUTION ALSO GIVES CREDENCE TO THE MORE SOUTHERN ECMWF AND UKMET
MODELS.
This scares me
19:15UTC, 22:15UTC 1:45 UTC (current frame floater) Southern eyewall at same latitude all three frames hours apart...... Northern eyewall at same 19:15 UTC and 22:15UTC........at 1:45 UTC (current) nearly 2 tenths of degree south. Its not a coincidence that the eyewall just "happened" to contract at an oddball southward wobble. Its the contraction that gave that appearance...go to the fricken floater run the loop and press your zoom button until you get it (southern eyewall) lined up horizontally with a stationary point and RUN IT............ and dont call me dude nor speak to me like I am an idiot.
DISAGREEMENT TO INDICATE A WESTWARD TURN IN THE FORECAST.
They want to head it west but not yet
WTNT41 KNHC 130248
TCDAT1
HURRICANE IGOR DISCUSSION NUMBER 20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010
1100 PM AST SUN SEP 12 2010
IGOR HAS CONTINUED TO INTENSIFY WITH VERY COLD CLOUD TOPS...LOWER
THAN -70C...WRAPPING AROUND THE SLOWLY-SHRINKING EYE DURING THE
PAST SEVERAL HOURS. ALTHOUGH THE TOPS HAVE RECENTLY WARMED A
LITTLE OVER THE SOUTHWEST QUADRANT...SUBJECTIVE DVORAK ESTIMATES
FROM TAFB AND SAB ARE T6.5/127 KT AND OBJECTIVE ESTIMATES FROM THE
ADT AND HIE ALGORITHMS ARE T6.6/130 KT AND T6.9/137 KT...
RESPECTIVELY. AS A COMPROMISE...THE INITIAL INTENSITY IS SET AT
130 KT. AN EXPERIMENTAL PRODUCT FROM UW-CIMSS RUN AT NHC INDICATES
THAT THERE IS A 42 PERCENT CHANCE OF SECONDARY EYEWALL FORMATION
WITHIN THE NEXT 12 HOURS...AND A 90 PERCENT CHANCE WITHIN 24 HOURS.
THE PERIOD OF RAPID INTENSIFICATION IS LIKELY TO END SOON...BUT THE
OFFICIAL FORECAST FOLLOWS THE SHIPS/LGEM MODELS BY SHOWING IGOR
REACHING THE THRESHOLD OF CATEGORY 5 STRENGTH BEFORE THAT HAPPENS.
SOME WEAKENING IS THEN INDICATED AFTER EYEWALL REPLACEMENT
OCCURS...BUT IGOR IS EXPECTED TO REMAIN A POWERFUL HURRICANE FOR
SEVERAL DAYS. AS IS ALWAYS THE CASE WITH STRONG HURRICANES LIKE
IGOR...FLUCTUATIONS IN INTENSITY ARE LIKELY BUT ARE ALSO DIFFICULT
TO FORECAST.
THE MEAN MOTION IS 270/11...BUT IGOR HAS BEEN WOBBLING A LITTLE TO
THE SOUTH OF THAT VECTOR. IGOR IS MOVING INTO AN ENVIRONMENT WHERE
THE STEERING FLOW IS BECOMING INCREASINGLY DICTATED BY A LARGE
LONGWAVE TROUGH OVER THE WESTERN ATLANTIC...AND THE HURRICANE IS
EXPECTED TO RESPOND BY TURNING TOWARD THE WEST-NORTHWEST WITHIN THE
NEXT 24-48 HOURS. SOME OF THE GLOBAL MODELS INDICATE THAT THE
TROUGH COULD FLATTEN A LITTLE BY DAY 3 AND ALLOW THE SUBTROPICAL
RIDGE TO BUILD WESTWARD...BUT AT THIS TIME THERE IS TOO MUCH
DISAGREEMENT TO INDICATE A WESTWARD TURN IN THE FORECAST. THE
TRACK GUIDANCE HAS SHIFTED A LITTLE TO THE NORTH...BUT THE NEW
OFFICIAL FORECAST STILL LIES ON THE SOUTHERN SIDE OF THE GUIDANCE
ENVELOPE UNTIL IT BECOMES CLEAR THAT IGOR IS READY TO TURN. THIS
SOLUTION ALSO GIVES CREDENCE TO THE MORE SOUTHERN ECMWF AND UKMET
MODELS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 13/0300Z 17.6N 47.8W 130 KT
12HR VT 13/1200Z 17.8N 49.5W 140 KT
24HR VT 14/0000Z 18.2N 51.3W 135 KT
36HR VT 14/1200Z 18.9N 53.0W 130 KT
48HR VT 15/0000Z 19.8N 54.6W 125 KT
72HR VT 16/0000Z 22.0N 57.5W 125 KT
96HR VT 17/0000Z 24.0N 60.0W 120 KT
120HR VT 18/0000Z 27.0N 63.0W 110 KT
$$
FORECASTER BERG
In their discussion, the NHC says it was moving a little south of west.
THE SOUTH OF THAT VECTOR.
A westward turn will scare people...
They may not want to have a more westerly forecast yet but they need to be careful so as not to make the adjustment too much. So, naturally, they shift a hair to the right.
I put up the forecast tracks for 5 and 11 and there was not much difference in them.
## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/13/10 00 UTC ##
## PASSED SCREENING STEP, MIGHT BE ANNULAR, CALCULATE AHI FROM DISCRIMINANT ANALYSIS ##
## AHI= 1 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
Julia being the 10th named storm of the season, formed 1 day earlier than Jeanne did in 2004
we are now ahead of 2004s pace and 3 storms behind 1995, which had Marilyn develop on this date
There is no TD13.
The public has a responsibility upon itself, to listen for hurricane warnings during the season. NHC does a good job with their warnings - the cone and the long range forecasts are for pilots, ship captains, news media... No big deal to move the cone.
NHC takes it's role quite seriously when it's time to tell people to board up and hunker down.
Um what??
Yep -- wow
The blog has been going so fast, that its hard to post and read.
Igor is not set in stone yet obviously, but it is a long way away. Needs to be watched.
One could argue they did that with Katrina and Ike, among others. I'm not highly confident in this forecast track but it, so far, doesn't look as far right of track as Earl wound up being.
- - - MAXIMUM WIND SPEED (INTENSITY) PROBABILITIES - - -
VALID TIME 12Z MON 00Z TUE 12Z TUE 00Z WED 00Z THU 00Z FRI 00Z SAT
FORECAST HOUR 12 24 36 48 72 96 120
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
DISSIPATED X X X X X X 1
TROP DEPRESSION X X X X X 1 2
TROPICAL STORM X X X 1 3 6 23
HURRICANE 99 99 99 99 97 93 74
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
HUR CAT 1 X X 2 6 13 21 32
HUR CAT 2 X 1 5 14 19 23 21
HUR CAT 3 2 14 29 40 35 31 16
HUR CAT 4 54 64 51 32 24 15 4
HUR CAT 5 44 20 13 8 6 3 1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
FCST MAX WIND 140KT 135KT 130KT 125KT 125KT 120KT 110KT
the formatting's messed up though.
good point about 1995
As a first responder I can tell you that they will hold off until they are absolutely certain there will be some impact. The logistics involved in moving people to places is quite expensive, and I tell you this in the interest of full disclosure--money talks. Until such time as is reasonably necessary, they will be conservative.
Link
That's old news. ;)
Obviously the entire eyewall contracted, however the eyewall contraction was to the south. That is, the northern part contracted south but stayed the same from an angular perspective. The southern part of the eyewall did not contract north but instead became steeper or tighter from an angular perspective.
Obviously this is how it appears to me, by no means am I communicating directly with the weather gods.
Dang. Came back from the store and thought I found something big.
StormW:
"If it's strong enough, and oriented in a certain way, it can, well, not really create it's own high pressure, but it can what we call "pump the ridge"...meaning, if there is a decent enough ridge to it's north, if the outflow of the hurricane is strong enough, the heat it pumps out, will reinforce the ridge to the North and NW of the hurricane enough, that it has a tendency to remain on a more of a WNW or even steady NW course, vice a more poleward motion. That is what we mean when we say the a strong hurricane can modify the environment around it."
Max Mayfield:
A large and strong hurricane can on occasion contribute to building a ridge to the north. Hurricane Gilbert in 1988 was such an example. Some of the models continued to indicate it would turn more toward the north in the Gulf of Mexico and it continued moving west-northwestward instead. Hopefully, the numerical models have improved enough to handle this much better. Examples like Isabel in 2003 and Bill in 2009 turning northward were handled well by the models.
Viewing: 3201 - 3251
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