Thrawst's WunderBlog

What happened to StormW?; Quick update on the Tropics

By: Thrawst, 3:33 PM GMT on September 19, 2010

:S, He is gone. How did he get banned?

Hurricane Igor is steadily weakening, partially due to shear, partially due to dry air, and partially due to inner core disruption as a blend of the previous reasons.
Maximum sustained winds are about 85 MPH, according to the NHC. I believe it will directly impact Bermuda as an 80 MPH hurricane. Bermuda, stay safe!

Tropical Storm Julia is amazingly hanging in there with Maximum sustained winds of 50 Mph. It unexpectedly modestly intensified 5 knots last night, and seems to be holding its vigor. ALthough, by 5 PM, I expect the final demise of Julia, and let her become a remnant low in 36 hours. What an amazing storm that was.

Invest 94L is on the verge of becoming a TD. Good convection, and good banding features. Most of the models are are unorthodox, and I believe this is because it is not developed yet.

Alright everyone have a good one!
Thrawst

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Tropical Weather Analysis - September 16, 2010 Issued 7:20 PM

By: Thrawst, 11:22 PM GMT on September 16, 2010

Major Hurricane Igor has the characteristics of a Category 3 Hurricane, albeit a rather large one. Tropical storm force sustained winds extend 290 miles from the center of Igor, and hurricane force winds extend 105 miles from the center. Comparing that to of Hurricane Katrina of 2005, it is nearly as large in the diameter of tropical storm force winds. I expect the wind field to continue to expand, and perhaps become a Top 5 largest hurricane within the next 36 - 48 hours.



The 35th Advisory on Hurricane Igor is as follows:

HURRICANE IGOR DISCUSSION NUMBER 35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010
500 PM AST THU SEP 16 2010

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REACHED THE CENTER OF
IGOR AROUND 1600 UTC. THE HURRICANE HUNTERS MEASURED A MINIMUM
PRESSURE OF 940 MB AND MAXIMUM FLIGHT-LEVEL AND SFMR WINDS OF 130
AND 98 KT...RESPECTIVELY. SINCE THAT TIME..THE CLOUD PATTERN
ASSOCIATED WITH IGOR HAS CHANGED LITTLE IN ORGANIZATION...AND
DVORAK T-NUMBERS REMAIN AT 5.5 FROM SAB AND TAFB. BASED UPON THE
AIRCRAFT DATA AND THE LOWER SATELLITE INTENSITY ESTIMATES...THE
INITIAL INTENSITY IS REDUCED TO 110 KT. THE EXTENSION OF AN
UPPER-LEVEL TROUGH PASSING NORTH OF IGOR IS STILL PRODUCING ABOUT
15 KT OF WESTERLY SHEAR OVER THE CYCLONE...ACCORDING TO THE LATEST
UW-CIMSS ANALYSES. THE SHIPS MODEL OUTPUT SHOWS A REDUCTION IN THE
SHEAR WITHIN THE NEXT 12 HOURS AS THIS FEATURE MOVES AWAY...WHICH
COULD ALLOW AN OPPORTUNITY FOR SOME RE-INTENSIFICATION IN THE
SHORT-TERM. THE GUIDANCE INDICATES THAT IGOR WILL BE MOVING INTO AN
ENVIRONMENT OF GRADUALLY INCREASING SOUTHERLY TO SOUTH-
SOUTHWESTERLY SHEAR IN ABOUT TWO DAYS...AND OVER COOLER WATERS BY
THE END OF THE FORECAST PERIOD. THE COMBINATION OF THESE TWO
FACTORS SHOULD RESULT IN A SLOW WEAKENING BEYOND 48 HOURS...AND THE
NHC OFFICIAL FORECAST REFLECTS THIS. BY DAY 5...GLOBAL MODELS
INDICATE THAT IGOR WILL BE AT LEAST BEGINNING TO UNDERGO
EXTRATROPICAL TRANSITION.

IGOR CONTINUES TO MAINTAIN ABOUT THE SAME MOTION...310/7. THE
REASONING FOR THE TRACK FORECAST IS UNCHANGED. THE HURRICANE IS
FORECAST TO MOVE NORTHWESTWARD AND THEN NORTH-NORTHWESTWARD WITH
SOME INCREASE IN FORWARD SPEED AROUND THE WESTERN EXTENT OF A
SUBTROPICAL RIDGE DURING THE NEXT 48-72 HOURS. BEYOND 72 HOURS...
IGOR SHOULD BEGIN ACCELERATING WHILE TURNING NORTH AND THEN
NORTHEAST AHEAD OF AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH
MOVING THROUGH THE NORTHEAST U.S. AND CANADIAN MARITIMES. THE
LATEST MODEL GUIDANCE HAS SHIFTED TO THE LEFT THIS CYCLE APPARENTLY
DUE TO TIMING DIFFERENCES ASSOCIATED WITH THE AFORMENTIONED
SHORTWAVE TROUGH. THE OFFICIAL NHC TRACK FORECAST HAS BEEN NUDGED
WESTWARD...FOLLOWING THE MULTI-MODEL CONSENSUS...AND LIES IN THE
MIDDLE OF THE GUIDANCE ENVELOPE.

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I pretty much agree with the forecast discussion above. The next 2 days intensification will mainly depend on inner core structure, and Eye Wall Replacement Cycles can make fluctuations in the strength of the hurricane. I believe that at Day 4, shear will increase to around 20 - 25 knots from the South to Southwest, caused by a rather flat, zonal trough to its west. Therefore, I agree with the NHC intensity forecast.

INITIAL 16/2100Z 21.7N 58.1W 110 KT
12HR VT 17/0600Z 22.4N 59.2W 110 KT
24HR VT 17/1800Z 23.5N 61.0W 115 KT
36HR VT 18/0600Z 24.9N 62.7W 115 KT
48HR VT 18/1800Z 26.5N 64.0W 110 KT
72HR VT 19/1800Z 30.5N 65.5W 100 KT
96HR VT 20/1800Z 35.5N 62.5W 90 KT
120HR VT 21/1800Z 42.0N 53.0W 70 KT

Igor is rounding the southwestern periphery of the Subtropical Ridge. As such, a gradual bend towards the NW and NNW are expected in the next 3 - 5 days.

Bermuda better begin either evacuation orders, or preparation for a very large, and perhaps a multi-day event of at least tropical storm force winds.

I will continue to monitor Igor, and will make another update on Igor later tonight if necessary.

HURRICANE KARL:

As of 5:00 PM EST, the NHC's intensity states:

Location: 19.6°N 93.7°W
Max sustained: 80 mph
Moving: W at 12 mph
Min pressure: 977 mb

The Min Pressure for an 80 mph Category one hurricane is a little lower than normal, which proves my theory that the MSLP's in the Gulf and Caribbean are well below normal. Here in the Bahamas, the pressure is currently 1009 Millibars. Thats typical of a weak tropical depression, and we had an unbelievable day. Back on topic, Karl is gathering strength quite steadily. I believe once Karl sustains convection over its core for the next 6 hours, it could perhaps rapidly intensify, perhaps to a Category 3 Hurricane. My current thinking is a Category 2, 105 mph Karl at landfall in Mexico, ALTHOUGH I am predicting a 30% chance that Karl could rapidly intensify to a Major Hurricane, or Category 3 Hurricane.



HURRICANE JULIA:

Wow, how much more generous can the NHC get? I strongly believe Julia is a sheared, dissipating tropical storm. I predict it is a 60 mph sheared storm. I won't go into detail as I believe it will make no threat to land, and will curve out to sea, and affect Europe in a week to a week and a half.

ELSEWHERE:

The ECMWF continues the Cape-Verde train with yet ANOTHER tropical depression 2 - 3 days from now. This would practically recurve strait off the bat, as the weakness in the Subtropical Ridge affecting Julia and Igor are currently experiencing remains.

The GFS develops a tropical depression in 5 - 7 days in the Central Atlantic to East Caribbean, and this could be the beginning of Southwest Atlantic "mischief" as the Cape-Verde may start to slow down in 1 to 2 weeks.

DON'T THINK THE SEASON IS OVER AFTER THE TRAIN IS GONE, ACTIVITY WILL JUST SHIFT WEST.

Thrawst

Updated: 11:23 PM GMT on September 16, 2010

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Major Hurricane Igor Update - 7.20 PM

By: Thrawst, 11:26 PM GMT on September 12, 2010

As I suspected would happen, Hurricane Igor explosively intensified from a pressure of 988 MB at 5 AM, to 942 MB at 5 PM. Thats a drop of 46 MB in 12 hours, which is very impressive. If you do the math, thats an average of 3.8 millibar drop an HOUR. On a steady strengthening cyclone, you would get about 5 - 15 millibar drop in a day, if not less.

Based on this analysis, and recent microwave and satellite imagery, I suspect Igor will be a 145 - 150 MPH hurricane at 11 PM, with the possibly of a Category 5 status sometime tomorrow.

I put the odds of Igor hitting Category 5 status at 40%. Favorable environments at least for the next 3 days should allow strengthening to occur. Thereafter, some southwesterly shear is POSSIBLE, although this should only cause a SLOW weakening. Also, around Day 5, SST's should gradually start to cool, and the heat of the ocean shouldn't extend as great depth as where it is now (TCHP).







Thrawst

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Tropical Weather Analysis; 92L, TD-12, Hurricane Igor

By: Thrawst, 5:16 PM GMT on September 12, 2010

Although I said in previous blogs I was going to stop tropical updates, I feel it is necessary to create an analysis of the tropics, due to the rapidly increasing activity, and the possibility of having 3 storms active at the same time in 24 hours.

TROPICAL UPDATE:

Invest 92L is the closest to home (The Bahamas), so I will start with an analysis of it.

First off the basics of this wave:

- It is struggling with dry air, and mysterious waning of convection during the evening hours each day (I suspect this will happen at least one more time).

- It developed as a monsoonal low pressure system off the Central American coast.

- It is in an ideal environment other than dry air.

- The reason it is not developing more steadily is because it lacks a well-defined spin.

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As soon as Invest 92L develops enough spin (Which it is currently lacking), it can develop more steadily, due to perfect conditions, excluding dry air.


Figure 1. 850MB vorticity (Or spin). Notice the difference in vorticity in 92L and Hurricane Igor, and TD-12. TD-12 developed because more spin was created.


Figure 2. 12:00 PM image of Invest 92L

It seems as of 92L is a bit elongated southwest to northeast, signaling a still-to-develop tropical wave. Wind-shear is currently 10 knots, and will stay in the 5 - 10 knot range until it makes a landfall in the Yucatan Peninsula.



As far as track is concerned, I believe 92L will stay on a West track until it slams into the Yucatan Peninsula or Belize. It is certainly possible that 92L could briefly go WSW until it takes a more West track before it hits the Yucatan.

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Tropical Depression 12:

Tropical Depression 12 is still in its formative stages, but I suspect this system could be Julia by 5 PM. Right now I would have to agree with the NHC's intensity forecast.

INITIAL 12/1500Z 12.7N 21.4W 30 KT
12HR VT 13/0000Z 12.8N 23.3W 35 KT
24HR VT 13/1200Z 13.5N 25.5W 45 KT
36HR VT 14/0000Z 14.5N 27.7W 55 KT
48HR VT 14/1200Z 15.7N 29.4W 65 KT
72HR VT 15/1200Z 19.0N 32.5W 65 KT
96HR VT 16/1200Z 23.0N 37.0W 65 KT
120HR VT 17/1200Z 26.5N 43.0W 65 KT

Forecaster Brennan (The forecaster who created the first advisory on TD - 12), made a very interesting point.

THE DEPRESSION WILL BE MOVING
OVER WARM WATERS FOR THE NEXT COUPLE OF DAYS...AND STEADY
INTENSIFICATION IS FORECAST. BEYOND THAT TIME...THE CYCLONE WILL BE MOVING OVER MARGINAL SEA SURFACE TEMPERATURES...AND THE SHIPS MODEL SHOWS THE SHEAR INCREASING. THE STATISTICAL MODELS SHOW SOME WEAKENING AT DAYS 4 AND 5...BUT THE DYNAMICAL MODELS SHOW THEIR PEAK INTENSITY OF THE CYCLONE LATE IN THE PERIOD.

That is a great analysis of the future environment of TD - 12. I have to greatly agree with this forecast, and no explaining of the future environment is needed. Thank you Forecaster Brennan.

The only thing I have to mention is that the current peak the NHC has may be a bit conservative.






The track of TD - 12 is pretty simple. A small subtropical ridge extending from North Africa to the Eastern Atlantic, will continue to pin-point TD - 12 West to West-North-West for the next 12 - 24 hours. Thereafter, TD - 12 should round the ridge and head Northwest into the North Central Atlantic. Most models predict an amplification of another subtropical ridge to TD-12's West, which may be amplified by Hurricane Igor, and make TD - 12 turn back WNW later in the period.

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Hurricane Igor-

Hurricane Igor is RAPIDLY intensifying, increasing its winds from 80 MPH to 105 MPH in 6 hours, and an 18 millibar drop in pressure in the same amount of time. That is close to a phenomenon known as EXPLOSIVE INTENSIFICATION, although it needs to continue to intensify at the same rate for another 6 hours. As of 12:45 PM, it seems like Igor may be continuing to explosively intensify.



As far as intensity in the long term is sort of uncertain, but I expect a peak of at least 150 MPH, with a slim chance of reaching Category 5 status before curving out to sea.



I believe the track will again be shifted to the left (west) at 5PM. The trofs coming off the American Coast are quite zonal and flat, which will make curvature of Igor less sharp. So, I suspect Igor may take a similar track to Hurricane Earl, but perhaps a little bit more to the East.

Residents in Bermuda should monitor the progress of Igor Very Closely.

Otherwise in the tropics, a couple more waves are moving off the coast of Africa at days 3 and 7. These are moving off at a lower latitude, and thus, making curvature less likely.

The Cape-Verde wave train continues to show life, although this may soon end. We are getting towards the end of the Cape Verde train. HOWEVER, with La Nina, MJO, and NAO all in our area, the train may stay a bit longer than normal.

No other tropical cyclones are expected to develop in the next 48 hours.

Thrawst

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....Gaston Analysis

By: Thrawst, 12:44 AM GMT on September 06, 2010

Gaston Coming Back to life.



Although dry air is creating a detrimental aspect to Gaston, and will continue to be detrimental for another 12 - 24 hours, Gaston will move into a moister environment thereafter, with low wind shear as well.

Predictions:

Initial: Remnant Low 20KT
12HR: Remnant Low 25KT
24HR: TD-Gaston 30KT
36HR: TS-Gaston 35KT
48HR: TS-Gaston 45KT
60HR: TS-Gaston 55KT
72HR: H-Gaston 65KT
84HR: H-Gaston 70KT
96HR: H-Gaston 70KT
108HR: H-Gaston 75KT
120HR: H-Gaston 75KT

12 Hours: Ex-Gaston should slowly move into a moister environment and thus, more convection should start to develop.

24 Hours: Low wind shear and warm waters, and even moister air should contribute to a rejuvenation of Gaston. Convection should consolidate enough to be considered TD-Gaston.

36 Hours: Convection should continue to consolidate with some outflow creating ventilation which should let steady intensification occur after 36 hours.

48 Hours: With a TUTT feature to its west, ventilation to the west and north should continue, and let Gaston steadily intensify. Gaston should near the Lesser Antilles at around this time.

60 Hours: Gaston should continue intensifying as stated in 48 HOURS. Although I question how close Gaston may get to the mountainous terrain of Puerto Rico and Hispaniola. I will keep it generously at 55 Knots.

72 Hours: As Stated in previous time frame, I will continue to generously keep Gaston intensifying to a 65 Knot, Category 1 Hurricane. Although this may be a bit too generous.

84 Hours: This is where I say, "Ok, too many variable to forecast Gaston to continue steady intensification." I only modestly intensified Gaston to a 70 Knot, Category 1 Hurricane. By then, it could be around Haiti.

96 Hours: This is the same as 84 Hours. I am too cautious in intensifying Gaston, so my forecast is 70 Knots, Category 1 Hurricane at 96 hours.

108 Hours: Modest Intensification continues with Gaston, and I predict a 75 Knot hurricane, Category 1 Hurricane, at 108 Hours.

120 Hours: Too far out in advance to make any changes to the intensity. Gaston should be around central Cuba by Day 5.



SW GULF OF MEXICO INVEST 90L:

I don't expect a hurricane, but most likely a Tropical Depression by 11 AM tomorrow. It has a small chance of developing into a Tropical Storm, thus named Hermine, for about 24 - 36 hours from now, as it slowly moves NNW to NW.

Thrawst

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About Thrawst

I have been fascinated by severe and tropical weather since the 2004 season. What a season that was!! Also a wave swell freak!

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