Irene roars into life; may become the season's first hurricane

By: Dr. Jeff Masters , 12:03 AM GMT on August 21, 2011

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Tropical Storm Irene roared into life this evening, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. An Air Force hurricane hunter aircraft in the storm was finishing up its mission when it suddenly came across a region with intense thunderstorms and surface winds of 50 mph. The aircraft found that a center of circulation had barely closed off on the southwest edge of this region, though the plane found almost no winds from the west around the circulation center. The 6:10pm EDT center fix found a central pressure of 1007mb, which is quite high for the observed 50 mph winds. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. Infrared satellite loops and radar out of Martinique show the storm is poorly organized, with no evidence of spiral bands. The center of Irene is expected to cross over the Caribbean island of Dominica early Sunday morning, but the heaviest thunderstorms lie to the north of the center, and will affect Guadeloupe, Antigua, and St. Kitts and Nevis.


Figure 1. Evening satellite image of Irene.

The computer models have shifted southwards since yesterday, and now take Irene south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, Irene should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn Irene to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. We can expect that Irene will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether Irene's turn to the north will take the storm into the Gulf of Mexico or not. Irene most reminds me of Tropical Storm Fay of 2008. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Irene will be battling dry air and moderate wind shear of 10 - 20 knots through Sunday, and it will take the storm 1 - 3 days to build up an eyewall and intensify into a hurricane. Irene is more of a threat than Tropical Storm Emily of early August was, since Irene has closed off a center farther east than Emily did and has more time to organize before encountering Hispaniola. I don't think passage over Hispaniola will destroy Irene, since it is a fairly large storm, and is likely to be a hurricane by then. However, if Irene follows the NHC forecast, it will have an extended encounter with Hispaniola and Cuba on Tuesday through Wednesday that will probably weaken the storm below hurricane force. Keep in mind that the average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles. Irene could easily miss Florida and move up the East Coast and hit North or South Carolina, or pass through the Florida Keys and into Gulf of Mexico, ending up who knows where. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or U.S. coast, since Irene could well be paying you a visit as a tropical storm or hurricane sometime in the next week.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on northern Guatemala, Belize, and portions of Mexico's Yucatan Peninsula as the storm tracks westwards at 12 mph. Dissipation is expected Sunday as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Irene is the 9th named storm this year, and its formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 had an earlier date. The first eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 2. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. 98L has a long stretch of ocean to cross before it could affect any land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Jeff Masters

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Quoting P451:


So, let's use one that's a little more realistic then.




Well, nah, that one is pretty scary too. Solid -75 to -82C blob. Look at how well the system consolidated in the past few hours. The baby fat is almost entirely gone.



But there is almost nothing south of the center. May even be exposed.
Member Since: August 22, 2010 Posts: 0 Comments: 652
120. beell
Quoting Chicklit:
Would someone care to explain this?
...THERE IS NO CONVERGENCE OF NE AND SE TRADE
WINDS...THUS THERE IS NO ITCZ DEPICTED ON THE SURFACE ANALYSIS.

Also, haven't been able to keep up with the blog, but thought this was worth repeating from the 8 p.m. NHC update:
T.S. IRENE IS FORECAST TO MOVE ACROSS THE W TROPICAL ATLC THEN INTO THE NE CARIBBEAN SUN NIGHT. IRENE WILL THEN MOVE NEAR WINDWARD PASSAGE ON TUE TO OVER CUBA WED AND STRAITS OF FLORIDA ON THU. THE SURFACE RIDGE WILL GRADUALLY WEAKEN THROUGH MON.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE




The last two waves were large enough and strong enough to disrupt the "normal" ITCZ pattern of NE trades and the normal southeasterlies originating near the equator.
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llc removed from deep convection
Member Since: July 21, 2010 Posts: 0 Comments: 1108
I see we have Irene!.Let's hope she's all bark and no bite.
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Is Levi gone for the night? Have the grandson, kinda missed a lot.
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I realize that it is Saturday night, and I know they don't like interruptions, but I believe it is time to convene the DOOM:CON high council for a possible update to the DOOM level.
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What on earth do we have to do here in TX to get some rain? We need a Tropical Storm here bad to drop a few days worth of the wet stuff on us.
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Center is clearly visible on Antilles radar due east of Dominica.

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Quoting ClydeFrog:
Here in St. Thomas, will take pics and post when conditions warrant. If anyone would like updates let me know...
of coarse post them anyway good to hear from all of our island friends
Member Since: July 15, 2006 Posts: 170 Comments: 53462
Meanwhile... off to the EAST




A LARGE AND ELONGATED AREA OF LOW PRESSURE CENTERED JUST WEST OF THE
CAPE VERDE ISLANDS IS PRODUCING DISORGANIZED SHOWER AND
THUNDERSTORM ACTIVITY. THIS SYSTEM IS MOVING OVER COOLER WATERS AND
DEVELOPMENT IS BECOMING LESS LIKELY. THIS SYSTEM HAS A LOW
CHANCE...20 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS. LOCALLY HEAVY RAINS AND GUSTY WINDS WILL CONTINUE TO
AFFECT PARTS OF THE CAPE VERDE ISLANDS OVERNIGHT.
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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!



Yikes, and a trough digging down? Oh boy.
Member Since: October 8, 2008 Posts: 14 Comments: 4553
Well, the inching further west- or is that just me?
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Quoting GTcooliebai:
Here's a wonderful site for all your computer model wonders Link enjoy ;)


Thanks dude. Already bookmarked and referred to often. I never thought to share. A great service you preformed. Should come in handy, indeed.
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18z GFDL is showing quite a favorable environment for Irene ahead.
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While waiting for the 21August_12amGMT_ATCF (NHC's 12am position for Harvey is 17.3n89.5w)

TS.Harvey_6pmGMT_ATCF : Starting 19August_6pmGMT and ending 20August_6pmGMT

The 4 longer line-segments represent TropicalStormHarvey's path and
the shortest line-segment is the straightline projection back to the shoreline.

Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 12pmGMT then 6pmGMT :
TS.Harvey's travel-speed was 14.8mph(23.9k/h) on a heading of 283.7degrees(WNW)
TS.Harvey made landfall upon Dangriga*Belize(16.984n88.227w)
then 5miles(8kilometres) later at 6pmGMT passed over the airport* at Melinda
heading toward the northernmost section of the MayaMountainRange of Belize and Guatamala.

Copy&paste 16.1n84.0w-16.1n84.7w, 16.1n84.7w-16.3n85.7w, 16.3n85.7w-16.7n87.0w, 16.7n87.0w-17.0n88.3w, mdb, 16.7n87.0w-16.984n88.227w into the GreatCircleMapper for more info

* ie As near to as can be described using a single decimal point in the coordinates. If Harvey had had an eyewall, it would have passed over both locations.

The previous mapping (for 20August_12pmGMT)
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Quoting P451:


So, let's use one that's a little more realistic then.




Well, nah, that one is pretty scary too. Solid -75 to -82C blob. Look at how well the system consolidated in the past few hours. The baby fat is almost entirely gone.



Where would you pinpoint the COC in that picture?

TIA
Member Since: April 19, 2011 Posts: 0 Comments: 157
Quoting KennyNebraska:


Put up "The Chart" then so I can see it please.


The colors were all wrong. I think this is it. :)

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were exactly is the center at thr present time?
Member Since: July 21, 2010 Posts: 0 Comments: 1108
Thanks, Doc. Guess SE USA is about 75% chance of getting hit by anyform of cyclone. Just went back on from helping my dad cleaning the boat (yes, it's with us in Raleigh), just to find out that some of models are predicting Category 4/5 storm. WTH?
Member Since: August 1, 2011 Posts: 28 Comments: 7961
Quoting JLPR2:
Well now, this image makes Irene look scary.

So does this.
Member Since: July 7, 2010 Posts: 0 Comments: 5672
Hey everyone, I have been on this site for years mostly as a lurker. I have a question for some of experts on here. Normally I wouldnt be at that worried but I live in Palm Beach County and my husband is heading out of town on business tomorrow and won't be back till Friday. I have 2 kids (ages 1 and 3). I have a 6 bedroom 2 story house that will take me at least 2 days to shutter if I can't find someone to hire and do it for me. How concerned should I be and when do you think we are going to have a better idea exactly where, when and strength?
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Quoting chrisdscane:
when do the next set of models come out?
Quoting Thrawst:
Interesting to see the next set of model runs now the Irene has indeed formed. Maybe leaning to the right?



when do thoose come out?
Member Since: July 21, 2010 Posts: 0 Comments: 1108
Thanks, Doc!

Leaving open the East Coast/NC scenario let's us all know to beware, as it is way too early to get a fix!
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Thanks, Dr. Masters...
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Link

Wind Probability
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aren't we close to dmin right now for Irene?
Member Since: April 19, 2011 Posts: 0 Comments: 157
First Dvorak Estimates for Irene
UW-CIMSS Automated Satellite-Based
Advanced Dvorak Technique (ADT)
Version 8.1.3
Tropical Cyclone Intensity Estimation Algorithm


Current Intensity Analysis




UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 20 AUG 2011 Time : 231500 UTC
Lat : 14:59:04 N Lon : 58:54:47 W


CI# /Pressure/ Vmax
2.8 /1004.5mb/ 41.0kt


Final T# Adj T# Raw T#
2.8 2.8 2.8

Center Temp : +4.2C Cloud Region Temp : -39.9C

Scene Type : USER DEFINED INITIAL CLASSIFICATION
Maximum CURVED BAND with 0.44 ARC in LT GRAY
at Lat: 14:34:47 N Lon: 57:54:35 W

Positioning Method : FORECAST INTERPOLATION
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Here in St. Thomas, will take pics and post when conditions warrant. If anyone would like updates let me know...
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Quoting 900MB:


Is that a "mark" well north of 16N?
yeah its the centre mark of image right in the area of deep convection
Member Since: July 15, 2006 Posts: 170 Comments: 53462
Interesting to see the next set of model runs now the Irene has indeed formed. Maybe leaning to the right?
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Would someone care to explain this?
...THERE IS NO CONVERGENCE OF NE AND SE TRADE
WINDS...THUS THERE IS NO ITCZ DEPICTED ON THE SURFACE ANALYSIS.

Also, haven't been able to keep up with the blog, but thought this was worth repeating from the 8 p.m. NHC update:
T.S. IRENE IS FORECAST TO MOVE ACROSS THE W TROPICAL ATLC THEN INTO THE NE CARIBBEAN SUN NIGHT. IRENE WILL THEN MOVE NEAR WINDWARD PASSAGE ON TUE TO OVER CUBA WED AND STRAITS OF FLORIDA ON THU. THE SURFACE RIDGE WILL GRADUALLY WEAKEN THROUGH MON.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE


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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!




wow
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when do the next set of models come out?
Member Since: July 21, 2010 Posts: 0 Comments: 1108
Is it me or do the models seem to be pretty well in agreement on this one? Im in SW FL and don't like to see that. I've seen models that go over us and then hours later are totally different, but this one they seem to just pinpoint Florida. ?
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84. IKE
GMZ089-210330-
SYNOPSIS FOR THE GULF OF MEXICO...AMENDED FOR T.S. IRENE INFO
430 PM CDT SAT AUG 20 2011

.SYNOPSIS...T.S. HARVEY INLAND OVER BELIZE NEAR 17.2N 88.8W AT
2100 UTC MOV WNW 11 KT. HARVEY WILL MOVE ACROSS GUATEMALA
TONIGHT...WEAKEN TO A TROPICAL DEPRESSION OVER MEXICO SUN AND
DISSIPATE SUN NIGHT. WINDS AND SEAS INCREASE BAY OF CAMPECHE
SUN. WEAK RIDGE ELSEWHERE THROUGH FORECAST PERIOD. TROPICAL
STORM IRENE 14.9N 58.5W AT 2300 UTC MOVING W OR 280 DEG 19 KT.
MAXIMUM SUSTAINED WINDS 45 KT GUSTS 55 KT. IRENE IS FORECAST
TO MOVE THROUGH CARIBBEAN TO THE STRAITS OF FLORIDA NEAR 24.0N
79.5W BY THU. WINDS AND SEAS INCREASE E GULF THU.
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Quoting JLPR2:
Well now, this image makes Irene look scary.
you guys best be getting ready
Member Since: July 15, 2006 Posts: 170 Comments: 53462
Quoting KEEPEROFTHEGATE:
T.C.F.W.
09L/TS/I/CX
MARK CENTRE FIX
16.63N/57.69W


Is that a "mark" well north of 16N?
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Thanks Dr. Masters.
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Quoting Tazmanian:
hey dfwstormwatch you still out there i need too se more mode runs you post
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Quoting Walshy:
Excellent blog.


hi!!! Anonymous
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Quoting PcolaDan:


No, he posted a chart, not The Chart. ;)


Put up "The Chart" then so I can see it please.
Member Since: July 7, 2010 Posts: 0 Comments: 474
Member Since: July 15, 2006 Posts: 170 Comments: 53462
Well now, this image makes Irene look scary.
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Quoting HoustonTxGal:


Ah ha, thanks!
no problem, you're welcome.
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Quoting KEEPEROFTHEGATE:
T.C.F.W.
09L/TS/I/CX
MARK CENTRE FIX
16.63N/57.69W

What means that?
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Quoting HoustonTxGal:


Where are you getting these?? just wondering.. would like to visit the site.

Thanks!
http://raleighwx.americanwx.com/models.html

Bottom-right side of the page.

Quoting HurricaneDevo:


Which model is this, and is that 920 I see in there?
18z GFDL. And yeah, 920mb.

Quoting KennyNebraska:


Yeah, you know in order for it to happen, Irene will have to experience the Atlantic high all the way through the next four days, with barely any influence from the trough that is supposed to be at full amplitude over the east CONUS some few days from now.

How likely is that?
Not the most likely solution IMO, especially with how much the GFDL strengthens it. Usually, such an intense cyclone will feel the weakness created by troughing more so than a weaker cyclone. Still a possibility however.
Member Since: September 2, 2009 Posts: 130 Comments: 21098
Evening everyone! For those that use i just got my site updated with all the Graphics and Models on Irene. I also moved all the Interactive Floaters over to Irene and took all the Floaters off Harvey. I can only put 5 Floaters up without slow some computers down.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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