Outlook for the remainder of hurricane season

By: Dr. Jeff Masters , 1:18 PM GMT on October 15, 2009

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Atlantic tropical cyclone activity finishes its peak phase in mid-October, and takes a major downturn after about October 20 (Figure 1). Since the current active hurricane period began in 1995, the last half of October through the end of hurricane season has given birth to an average of 1.7 named storms, 0.8 hurricanes, and 0.3 intense hurricanes. These numbers are nearly double the long-term climatological averages for the past 100 years. So far this year, only one tropical storm has hit the U.S.--Tropical Storm Claudette. If no more tropical storms make landfall in the U.S., it will be the first year since 1993 to see only one tropical storm hitting the U.S.


Figure 1. Atlantic hurricane season activity over the past 100 years.

Late October and November storms tend to form from tropical waves that come off the coast of Africa, or from the remains of old fronts that push off the coast of the U.S. As we can see from the track plot of all last half of October storms (Figure 2), there is a lot of activity during the period, but relatively few storms form out near the African coast. The water temperatures off the coast of Africa are starting to cool and be marginal for hurricane formation, and the African Monsoon is waning, leading to fewer African waves coming off the coast. Wind shear is also starting to increase, as part of its normal fall cycle.

Climatology of late-season major hurricanes
Let's examine the possibilities of getting a late-season major hurricane, since those are the storms we care most about. Since 1960, there have been twelve hurricanes that have existed as major Category 3 or higher storms after October 15. Eight of these have occurred since 1995: Omar of 2008 (Cat 4, Lesser Antilles), Paloma of 2008 (Cat 4, Cayman Islands and Cuba), Wilma of 2005 (Cat 4, Mexico; Cat 3, SW Florida), Beta of 2005 (Cat 3, Nicaragua), Michelle of 2001 (Cat 4, Cuba), Lenny of 1999 (Cat 4, northern Lesser Antilles), Mitch of 1998 (Cat 5, Honduras), and Lili of 1996 (Bahamas, Category 3). The other four were Joan of 1988 (Cat 4, Nicaragua), Kate of 1985 (Cat 3, Gulf of Mexico), Ella of 1962 (Cat 3, west of Bermuda), and Hattie of 1961 (Cat 4, Belize). Wilma of 2005 was the only major hurricane since 1960 to hit the U.S. after October 15. The highest risk region for late season major hurricanes is the Western Caribbean, along the coasts of Nicaragua, Honduras, Belize, Mexico, and Cuba. So, we can say with high confidence that most of the U.S. coast can relax. Only the west coast of Florida, Florida Keys, and South Florida need to still be concerned about the possibility of a major hurricane. The Lesser Antilles Islands, Puerto Rico, and Hispaniola are also at low risk for a major hurricane the remainder of the season.



Figure 2. Tracks of all tropical storms and hurricanes since 1851 that formed October 16-31.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are 0.5 - 1.5°C above average over the Western Caribbean and Gulf of Mexico (Figure 3), the primary formation areas for late October storms. So, there is still plenty of fuel for a major hurricane to form. Note also the tongue of warmer than average SSTs extending out into the Pacific Ocean from the coast of South America, the signature of weak El Niño conditions.


Figure 3. Sea Surface Temperature (SST) departure from average for October 15. Image credit: NOAA.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation by tearing a storm apart. Wind shear 10 knots and lower is very conducive for tropical storm formation.

The jet stream in mid-October is more active and extends further south, which brings higher levels of wind shear to the Atlantic. The more active jet stream also acts to recurve storms more quickly. Any system penetrating north of about 20 degrees north latitude we can expect to recurve quickly to the north and northeast this late in the season. The most recent 16-day forecast from the GFS model predicts a period of high wind shear over the tropical Atlantic over the next ten days (Figure 4). Beginning on October 25, wind shear is expected to fall again over the Western Caribbean, and we need to be alert for tropical storm formation then. Indeed, the latest run of the GFS model is predicting a large area of surface low pressure will form in the Western Caribbean during the last week of October, an indication that hurricane season may not be over yet.

El Niño
El Niño conditions, which typically bring higher wind shear to the Atlantic and interfere with hurricane formation, continue to be present in the tropical Eastern Pacific. It is probably the case that some of this year's inactivity can be attributed to El Niño. However, as I discussed in a post earlier this year, El Niño events that warm the central Pacific more than the eastern Pacific (called "modiki" El Niño events), tend to bring less wind shear to the Atlantic. In recent weeks, El Niño conditions in the Eastern Pacific have trended more towards a "modiki" type event, with a large amount of warming in the Central Pacific. This shift in the El Niño may bring lower wind shear to the Atlantic over the final month of hurricane season.


Figure 4. Wind shear forecast for October 23, 2009, as produced by the 00 UTC run on October 14, 2009 made by the GFS model. Wind shear below about 8 m/s (roughly 15 knots, red colors) is typically needed to allow tropical storm formation. There aren't too many red-colored areas over the prime breeding grounds for tropical storms in the Atlantic over the next ten days in this forecast.

Summary
Given how quiet the tropics are at present, and the forecast of a high wind shear regime lasting until October 25, I doubt any tropical storms will form over the next ten days. If we do get something, it would probably be in the middle Atlantic between Bermuda and the Azores, far from land. However, I am still wary of the possibility of a hurricane in the Caribbean the last week of October or in November this year. There is evidence that the Atlantic hurricane season is starting earlier and ending later in recent decades. Dr. Jim Kossin of the University of Wisconsin published a paper in 2008 titled, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is a "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high". We had two major hurricanes in the Caribbean after October 15 last year, and I give a 60% chance that we'll get a named storm in the Caribbean before hurricane season ends on November 30. Hurricane season is not over--it's just in hibernation.

Happy Valley to become Yucky Valley
Winter is fast approaching, and the season's first major snowstorm for the U.S. East Coast is coming this weekend, according to the wunderblog of Wunderground's Dr. Rob Carver. Conditions will be particularly nasty on Saturday in Happy Valley, where Penn State is situated. The surrounding hills may get 4 - 12 inches of snow, and rain mixed with snow with 36°F temperatures are expected for Saturday's Penn State - Minnesota game. Ugh, winter! I'll have a forecast for the coming winter in a post sometime in the next week.

The Senate has not yet voted on the proposal to cut NOAA funding. I will post a report when the vote occurs.

Jeff Masters

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Dr M's plot with the SST anomaly is a little misleading. Water 1.5C over "normal" SST doesn't dictate favorable conditions, raw values do.

Much of the coastal northern GoM waters only marginally favorable (water depth related TCHP questions aside). The reds in this plot are where it really is quite favorable.

Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting timtrice:
EPAC wave looking very promising:



I know some of you will think I'm crazy but it seems very easy to anticipate this being a storm within 24 hours and a major hurricane within 72.

I can agree with that...and the part about you being crazy...
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting shred3590:
Does anyone have a recommendation for good freeware for downloading and keeping data from a weather station? The software that came with my station only keeps 24 hours.


Weather Display


Good afternoon all
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EPAC wave looking very promising:



I know some of you will think I'm crazy but it seems very easy to anticipate this being a storm within 24 hours and a major hurricane within 72.
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133. 789
Quoting tornadodude:


yeah! haha I'm very excited
dont be late for work on the first day . sounds like it will be a good edumacation
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Quoting NRAamy:
saw Al Gore get questioned last night...it seems the population of the polar bears is BIGGER THAN EVER....it's GROWING...not diminishing....

so stuff that in your Prius and smoke it, Al.....


I'm no Al Gore hater, but doesn't he drive an SUV and have a really high electric bill for his mansion. What's the saying about take care of the plank in your own eye before you worry about the sliver in someone else's eye or something like that?
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Quoting Patrap:
Cranked up the floor furnace to burn off the ol summer..


.ack,coff..spit

Smoke alarms good to go too.

LOL. And people wonder why I fire mine up for 5-10 minutes in July...
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129. JRRP
2006

2009
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Quoting StormW:


????
Quoting TampaSpin:


Total BS what the government wants us to believe StormW...why is the stock market going up....anyone ever wonder. Its called TARP MONEY flooding the market. People don't understand what happened to all the TARP money....it was put back into the Market to drive the market. Its that simple.
You should stick to weather. I work in the stock industry and Tarp has helped improve things because that is what is was designed to do. The stock market was on the brink of collapse and Tarp had a big hand in steadying the ship. Now we need the job market to come alive and possibly a second stimulus package. Tarp is not the driving force behind the stock market. The market is looking 6-9 months down the road and sees things getting better including the housing and job market.
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LOL the scream matches. Thats where most of my ignore list came from. I usually retire to a diffrent blog when it gets cranking.


BTW Hello NE, Flood, Storm.

I be on anothern few minutes then I'll be signed off until the 26th. Wedding tomorrow then Cancun on Saturday =) Hopefully the weather window opens up and I dont spend most of the day stuck in the airport.
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Quoting TampaSpin:


There aren't any GW debates! Just people screaming at each other.


Here's your indisputable evidence of global warming... (just kidding)

Weather Underground Email Service for Miami, FL
Public Information Statement as of 1:12 PM EDT on October 15, 2009

...Record consecutive streak of 90-plus degree highs in Miami...

At 104 PM today, the high temperature at Miami International Airport
reached 90 degrees. This Marks the 11th consecutive day of high
temperatures reaching or exceeding the 90 degree mark, which ties
the all-time consecutive number of 90-plus degree days for the month
of October.

High temperatures are once again expected to hit or surpass 90
degrees on Friday ahead of a cold front moving into North Florida.
If the forecast pans out, a record number of consecutive 90-plus
degree highs for the month of October would be set for Miami. The
cold front will move through Southeast Florida Saturday afternoon,
putting an abrupt end to the unusual October heat wave.

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Cranked up the floor furnace to burn off the ol summer..


.ack,coff..spit

Smoke alarms good to go too.
Member Since: July 3, 2005 Posts: 428 Comments: 129841
Quoting tornadofan:


Wow - LUCKY - LOL


yeah! haha I'm very excited
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Quoting tornadodude:


I'm working for the Earth and Atmospheric Science Department at Purdue and am supposed to input weather data into computers, maintain software, and web pages for the department


Wow - LUCKY - LOL
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Does anyone have a recommendation for good freeware for downloading and keeping data from a weather station? The software that came with my station only keeps 24 hours.
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yup I will be. Especially for winter storms.
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Quoting TampaSpin:


There aren't any GW debates! Just people screaming at each other.


Yeh,your right,I don't stay around long enough to catch all the screaming,I disappear as soon as one starts.
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Quoting tornadofan:


What exactly will you be doing?


I'm working for the Earth and Atmospheric Science Department at Purdue and am supposed to input weather data into computers, maintain software, and web pages for the department
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Quoting NEwxguy:
I enjoy staying in here through the winter months,love the coastal updates from Storm,talking winter storms with bone and sulli and the other Northeast folks,of course you have keep dodging the GW debates that flair up,but I'm getting pretty good at that.


There aren't any GW debates! Just people screaming at each other.
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Quoting tornadodude:
well, I go to my first day of work for my new job at 2:15, pretty excited xD


What exactly will you be doing?
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Quoting NEwxguy:
I enjoy staying in here through the winter months,love the coastal updates from Storm,talking winter storms with bone and sulli and the other Northeast folks,of course you have keep dodging the GW debates that flair up,but I'm getting pretty good at that.


I definitely plan on being on in the winter, especially since my parents will be in upstate New York all winter, and I'll be up there for Christmas, and actually probably going to Boston for a day while I'm up that way
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I enjoy staying in here through the winter months,love the coastal updates from Storm,talking winter storms with bone and sulli and the other Northeast folks,of course you have keep dodging the GW debates that flair up,but I'm getting pretty good at that.
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well, I go to my first day of work for my new job at 2:15, pretty excited xD
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Quoting Bonedog:
Yea NE I missed the lightning one on discovery. really wanted to see it.

Hows the weather up your way? Snowing here =)


Bone i know you really want to stay up there...LOL
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Quoting StormW:


Yea...Bone and NE probably be pretty regular when the winter weather cranks up.


I'm glad to see that you stick around, Storm...
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Quoting catman306:
Question:
Hurricanes are fueled by high sea surface temperature and solar energy. Without hurricane formation, what happens to the energy? Does it stay in the tropics giving the next year a boost in starting temperatures (and potentially worsening the following year's hurricane conditions)? Or does it help produce more non-hurricane storms that keep coming long after hurricane season is through?


I'm guessing that to some degree, both ideas are true...some of that heat lingers, making for quicker and deeper SSTs the following year, but on the other hand, remember that for the most part, weather is the atmosphere looking for equilibrium, both in pressure and temperature (over simplified, I know, but essentially true)...
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Funny if our Gov. would have taken the 1.5tril. and divided it amoung every US citizen in the US.....each baby, child, and adult would have receieve nearly $5000 apiece....that would have been $25000 in my house hold....i think i would have stimulated the economy with that.....LOL
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Question:
Hurricanes are fueled by high sea surface temperature and solar energy. Without hurricane formation, what happens to the energy? Does it stay in the tropics giving the next year a boost in starting temperatures (and potentially worsening the following year's hurricane conditions)? Or does it help produce more non-hurricane storms that keep coming long after hurricane season is through?
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Bone,nothing going on right now,cloudy and cold,all our action starts tonight,the cape and the islands are really going to get hit hard I think on both these storms.
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Howdy, everyone, by the way...good to see Bone in here so frequently...
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Quoting Bonedog:
Yea NE I missed the lightning one on discovery. really wanted to see it.

Hows the weather up your way? Snowing here =)


How I envy you your snow...though the long range from the mets here indicate a colder rougher winter than normal
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Yea NE I missed the lightning one on discovery. really wanted to see it.

Hows the weather up your way? Snowing here =)
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Quoting ElConando:


Who then?


When trying to figure out who is backing legislation, first ask yourself, aside from the politician (who is receiveing "considerations" from the lobbyist), who stands most to profit from the law...and there you have your perpetrator
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Quoting Bonedog:
just read about this. Pretty awsome..

catatumbo lightning


Bone,
I saw a show on lightning on discovery channel and that was one of the things they showed,they had video,it was one of the most amazing things I've ever seen.Talk about a light show.
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DEVELOPING LOW, FORMER NEPARTAK (T0919)
40.0ºN 178.0ºE - 998 hPa

Subject: Developing Low In Sea South Of Aleutians
Member Since: May 24, 2006 Posts: 52 Comments: 46911
Quoting timtrice:


All in favor - AYE!


Well, don't get me wrong, I believe there is a great deal of Climate Change happening, but to give all of the opinions that confirm it while ignoring the data that proves otherwise is wrong...the truth is somewhere in the middle and changing the way we do things is a start, but let's try to figure out what's happening before we go off half cocked

As for calling it Global Warming, well that's misleading too...you warm up one area and the climate cools in another...how can you call that GW?
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Quoting Floodman:


Well, I'm with you...Al Baby likes to give you only the data that supports his position and then tell you that yes, Virginia, the sky IS falling...

It's like watching a documentary on UFOs where the opposing, skeptical view, is not represented at all; it makes you think that they'll be landing any minute now...that's crap science, no matter how you slice it


We're already here. Don't give it a second thought.

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Quoting StormW:


LOL!

I agree!!

My take on everything is, no matter what is voted for in Washington, be it healthcare, or whatever...you can be sure what ever decisions they make, they will make sure that folks somewhere are going to make a profit and have their pockets lined...and it ain't you and me.


Who then?
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I don't get PETA...

we have a monestary of Trappist monks here who supported themselves by selling eggs...PETA shut them down because of their alleged mistreatment of their chickens...

meanwhile...five miles from the monestary, my cousin raises 800,000 broilers at a time...

now...the monks had a heavily vested interest in caring for their chickens in such a way that they would continue to lay eggs...


while my cousin raises them for the expressed purpose of killing them, freezing them...and, presumably, frying them...

go figure....
Member Since: August 13, 2007 Posts: 0 Comments: 10492
TARP money turns into real money at some point anyway.
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Quoting Bonedog:
Already snowing by me =)

Hewitt, NJ 1305ft and WE HAVE SNOW!!!

Earliest I can remeber. NWS posted a winter weather advisory for me. 1 to 4 inches =)

LET IT SNOW
LET IT SNOW
LET IT SNOW


It's gotta be the global warming.
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Quoting StormW:


????


YOUR NOT BS.....the hole thing is BS....LOL
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I think this Winter Tallahassee will get snow flurries I can feel it!!!
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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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