Irene roars into life; may become the season's first hurricane
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
Reader Comments
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I see it now....
LOL...is it just me....or is the NHC contradicting themselves at the 11 PM discussion?....first they lean more west with their cone...yet make this statement about a further north reformation and Puerto Rico maybe needing a hurricane watch...this isn't making sense....
YES! We need a poll:
Where will Cantore be stationed in the US?
Nothing like that warm fuzzy feeling you get looking at the 4's & 5's on the Model tracks.
TS BUSTED FORECAST ALIBI
Deja vu?? not track wise exactly, but anyone remember hurricane irene of 1999, this was the first storm i can remember, i was 9 years old. (very sorry if this pic comes out too big, will remove if needed)
If just don't see PR avoiding severe conditions as well as the Northern Leeward and Virgin Islands. Irene's northern expansion is amazing.. is still getting wider each frame.
sorry could not help it lol
I'm hooked. I've been a member here for going on 6 years. There are times I can't tear myself from the screen. My latest obsession is the damn gfs model runs. I have to stay up to at least watch the late night screening lol . . . and certainly when it looks like a decent shot at affecting my neck of the woods.
For the record, SC hasn't been hit in the past 21 years. The East Coast hasn't been hit in the past five years... things that make you go hmm...
I saw the same contradiction..not bashing the NHC of course but I think they are covering their behinds in putting in that "however"
See...the GFS is already a bit off at the beginning of the loop with its central position of Irene...it needed to have start the run further NE...so I suspect that run is too far to the west with Irene by the end.....
I know I was here for the last big one "HUGO" and never wanna do it again!!
make sure your seat belts are buckled..this one will be a doozy..
There was also a famous play and movie, called "My Sister Irene" think it was written by Harvey,
Frankly, I don't buy GOM until the Euro starts shifting that way.
Wouldn't he almost have to be down on one of the Keys?
In terms of the HWRF? Way to much land interaction.
I just hope Irene doesn't change our east coast break...we are "overdue" though....whatever "overdue" means....
What worries me here is Irene may lean more NE in its projected path if she makes more reformation toward the convection....
The 00z GFS initialized at 8:00pm EST (aka 00z); we should start getting output from that 00z initialization soon though.
stop it
Conditions are perfect after land interaction is over for rapid intensification..There is a really good chance it occurs, but then again, forecasting rapid intensification is very hard.
No, the westward shift in the models.
I remember Irene (1999), I was in the ninth grade. Here in Orlando, it was extremely muggy the day before, then frequent rain and breezy that night. The day of, it was overcast with hardly any rain, but it was very gusty (peaked at sustained 38 gust 48 here)for the whole day as it hugged the coast.
Lol...Which is what I meant...
I was in Hollywood Beach taking a vacation on the beach for Irene. The forecast wasn't very accurate. Miami ran busses in the morning and thousands of people were caught in the storm with no way home when they cancelled all transportation.
It wasn't very pleasant being on the beach either - I thought the waves might go right over my little hotel and flood my room. And that wasn't much of a storm.
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