June hurricane season outlook and Arthur/Alma post-mortem

By: Dr. Jeff Masters , 2:35 PM GMT on June 02, 2008

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The season's first tropical storm, Arthur, has come and gone. Arthur formed Saturday afternoon--one day before the official start of hurricane season--and immediately made landfall in northern Belize on the Yucatan Peninsula. Arthur brought heavy rain to Belize, southeast Mexico, Guatemala, and Honduras. Resulting flooding in Belize has killed at least two people, left five missing, and flooded many homes and businesses. Rainfall totaled 171mm (about 7 inches) at Tikal International Airport in Northern Guatemala, and satellite rainfall estimates suggest as much as 10 inches of rain may have fallen in some isolated areas of southeast Mexico. Arthur's remains will continue to soak the region with up to six more inches of rain in the coming two days. No computer models are suggesting that Arthur's center will drift over any ocean areas and rise from the dead again. However, a new low pressure area (91E) has developed in the Eastern Pacific off the southeast coast of Mexico, just south of Arthur's remains. Moisture from Arthur/Alma may fuel the development of a third tropical storm--Boris--which could form Tuesday or Wednesday, and move northwestward into Mexico.

Before Arthur was a he, he was a she--Tropical Storm Alma in the Eastern Pacific. Alma soaked Costa Rica and Nicaragua with up to ten inches of rain, damaging or blocking 117 roads and destroying a number homes in Costa Rica, where an estimated 1,500 people are homeless. In Nicaragua, three people died, ten are missing, and 25,000 people are homeless in the wake of the storm.

June Atlantic hurricane season outlook
June is typically the quietest month of the Atlantic hurricane season. On average, we see only one named storm every two years in June. Only one major hurricane has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The highest number of named storms for the month is three, which occurred in 1936 and 1968. In the 13 years since the current active hurricane period began in 1995, there have been ten June named storms (not including this year's Arthur). Five tropical storms have formed in the first half of June in that 13-year period, giving a historical 38% chance of a first-half-of-June named storm.


Figure 1. Tracks of all June tropical storms and hurricanes since 1851.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are still quite cool in June, which limits the regions where tropical storm formation can occur. SSTs are typically too cold to allow storms to develop between the coast of Africa and the Lesser Antilles Islands, and there has only been once such development in the historical record (Figure 1). This year (Figure 2), SSTs are about 2°C above average off the coast of Africa, which has led to some unusually vigorous tropical waves for this time of year. SSTs near the Cape Verde Islands are about 25°C, and this will need to increase to at least 26°C before we need to be concerned about African tropical waves developing.

Typically, June storms only form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26°C-28°C, which is 0.5°C above average over most of this region. June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. Every so often, a tropical wave coming off the coast of Africa moves far enough north to act as a seed for a June tropical storm. This was the case for Arthur this year (which also had major help from the spinning remnants of the Eastern Pacific's Tropical Storm Alma). Another way to get Atlantic June storms is for a disturbed weather area in the Eastern Pacific Intertropical Convergence Zone (ITCZ) to push north into the Western Caribbean and spawn a storm there. This was the case for Tropical Storm Alberto of 2006 (which may have also had help from an African wave).


Figure 2. Sea Surface Temperature (SST) departure from average for May 29, 2008.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, the heat energy available in the tropical Atlantic has declined steadily since 2005, when the highest SSTs ever measured in the tropical Atlantic occurred. I expect that the TCHP will continue to remain well below 2005 levels this year, so we should not see any intense hurricanes in July, like we saw that year.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for May 31 2005 (top), May 31 of last year (middle) and May 31 2008 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is much lower. Image credit: NOAA/AOML.

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. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart.

Wind shear over the past 11 days (Figure 4) has been unusually low over the Gulf of Mexico, Caribbean, and Central America. Th shear was 4-8 m/s (8-16 knots) below average last week, aiding the formation of Tropical Storm Alma/Arthur. The jet stream is usually very active and quite far south in June, bringing plenty of shear. The jet stream looped unusually far northwards during late May, but is forecast to return to a more normal position over the coming two weeks, increasing the shear over the June breeding grounds for tropical storms. The jet stream will gradually weaken and retreat northwards as summer progresses, bringing lower wind shear and greater chances for tropical storm formation.


Figure 4. Top: Average wind shear over the 11 days ending on May 30. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation. Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note the unusually low wind shear area near Central America where Alma/Arthur developed. Image credit: NOAA/CPC.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast; this was a key reason why last year's Subtropical Storm Andrea never became a tropical storm.

Steering currents
The steering current pattern over the past few weeks has typical for June, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are well-predictable only about 3-5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the typical June pattern, bringing many troughs of low pressure off the East Coast capable of recurving any June storms that might form. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2005 pattern, that steered so many hurricanes into the U.S.

Summary
Recent history suggests a 38% chance of a named storm occurring in the first half of June. Given the current two-week wind shear forecast, the odds are that Arthur will be the only tropical storm we'll see during the first half of June. Still, there will be "holes" opening up from time to time in the shear pattern, so we need to keep our eye on the Gulf of Mexico and Western Caribbean. None of the computer models are forecasting tropical storm development in the coming seven days.

I'll have an update Tuesday afternoon, when the latest Colorado State University Atlantic Hurricane season forecast by Phil Klotzbach and Dr. Bill Gray will be available.

Jeff Masters

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707. condesa
1:08 AM GMT on June 03, 2008
Cuernavaca, Morelos
Lat/Lon: 18.9° N 99.2° W
We're southwest of Mexico City
706. condesa
1:05 AM GMT on June 03, 2008
No, it shuts down almost everynight and the only reason I can imagine for why it goes out during storms, which can get very intense here, is that they close the airport,?, or they disconnect electrical things... I don't know. It doesn't make sense.
The very first ever stations were installed in Toluca about 10 days ago- and they've got a real international airport... we don't typically get much advance warning, so that's why I was so surprised to see they shut down the ports over on the gulf already.
705. HurrikanEB
12:56 AM GMT on June 03, 2008
703.
when you say they shut it down during storms do you mean tropical storms and hurricanes or like thunderstorms...don't you need the weather station during those times?
where is Cuernavaca?
Member Since: May 2, 2008 Posts: 12 Comments: 1336
704. condesa
12:54 AM GMT on June 03, 2008
Sorry for the delays and distractions- I've been chasing a little kid around.
Weather service in Mexico is thinking that new tropical wave is going to make a storm here and that the anti-cyclonic spin is going to dissolve. I translate this, sortof, sorry.
About Stormy whatever... in spanish a storm is a tormenta. Sounds about right.
703. condesa
12:50 AM GMT on June 03, 2008
I came down here last year; I'm in Cuernavaca. Our only official weather station, which is about 20 miles from here, was down for 4-5 months because they closed the "international" airport because no none knew how a plane with a bunch of drugs landed, where it came from, who flew it... they re-opened it a couple of months ago, but I think they shut down the weather station when storms are coming in and at night when everybody goes home. Hardly anything is grounded here- electrically speaking...
702. thelmores
12:47 AM GMT on June 03, 2008
Looks like the convection on ALMA.... I mean Arthur......I mean Bertha.........well, whatever the hades you wanna call the thing entering the BOC.....

nice little flare up...... and I don't think its just a T-storm! LOL
Member Since: September 8, 2005 Posts: 0 Comments: 3805
701. HurrikanEB
12:41 AM GMT on June 03, 2008
682. MasterForecaster 12:15 AM GMT on June 03, 2008
Good evening CCHS, Everyone...

Looks like these are two circulations that do NOT want to die...does anyone know whats going on with the other waves?

Also...I've discovered how to prevent Hurricanes from striking the land, if anyone cares to ask...


How do you prevent hurricanes from striking land, MasterForecaster
Member Since: May 2, 2008 Posts: 12 Comments: 1336
700. IKE
12:32 AM GMT on June 03, 2008
Jeez..this late? Surprising........
Member Since: June 9, 2005 Posts: 23 Comments: 37858
699. WPBHurricane05
12:31 AM GMT on June 03, 2008
new blog up
Member Since: July 31, 2006 Posts: 56 Comments: 8112
698. katadman
12:29 AM GMT on June 03, 2008
IF Arthur were to reform in the GOM, NHC might rename him, but then again, they might not barther. lol
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697. Stoopid1
12:29 AM GMT on June 03, 2008
Wow, seems June has gotten off to an unusual start, perhaps even more son if Arthur's remnant low strengthens in the Bay of Campeche. I may go with the theme here (and my gut for some odd reason...) and say we could see Bertha in the next few days. If not, then this storm has been unique and tenacious either way. I just have a feeling this could be a groundbreaking storm.
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696. thelmores
12:29 AM GMT on June 03, 2008
#668

CCHS...... agreed 100%!
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695. Cavin Rawlins
12:28 AM GMT on June 03, 2008
Some very heavy rain amounts expected for parts of SE Mexico, Guatemala and El Slavador

Member Since: July 24, 2005 Posts: 407 Comments: 19076
694. 69Viking
12:27 AM GMT on June 03, 2008
690. XoendHoroeken 12:22 AM GMT on June 03, 2008

Not true when all along there has been two lows which are still visable on Satellite imagery.
Member Since: August 25, 2006 Posts: 1 Comments: 3022
693. weathermanwannabe
12:25 AM GMT on June 03, 2008
Good Evening Folks....
Member Since: August 8, 2006 Posts: 0 Comments: 9122
692. IKE
12:25 AM GMT on June 03, 2008
684. 69Viking 7:16 PM CDT on June 02, 2008
678. IKE 12:10 AM GMT on June 03, 2008

When did you move to South Central Mexico!?


LOL....no...I was agreeing with them saying I really appreciate Wunderground.....lol.....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
691. MasterForecaster
12:22 AM GMT on June 03, 2008
685. weatherblog 12:18 AM GMT on June 03, 2008
*682

Please don't say tunnels...lol


Well I think I missed the whole discussion on tunnels a few days ago, however it is not tunnels anyways.
690. XoendHoroeken
12:22 AM GMT on June 03, 2008
Wow. So at the beginning of all this we had the huge are of convection extending from the East Pacific into the Caribbean,

The convection associated itself enough in the Pacific to be named TS Alma.

Alma disorganized, lost its name and its remaining convection moved into the Caribbean.

Here it reconsolidated and was named TS Arthur.

Arthur moved further inland where it lost it name.

Some of the remaining convection moved into the Pacific where it may become TS Boris.

If Boris were to form it would likely move Nward eventually reaching the BOC.

In the BOC it would most likely strengthen to take on the name Bertha.

ALL OF THIS COULD OCCUR FROM GENERALLY THE SAME LOW. Now THAT would break some records!
688. GeoffreyWPB
12:20 AM GMT on June 03, 2008
Evening Weather...
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687. weatherblog
12:20 AM GMT on June 03, 2008
Be back later...
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686. Cavin Rawlins
12:19 AM GMT on June 03, 2008
Good evening all
Member Since: July 24, 2005 Posts: 407 Comments: 19076
685. weatherblog
12:18 AM GMT on June 03, 2008
*682

Please don't say tunnels...lol
Member Since: July 10, 2006 Posts: 27 Comments: 1623
684. 69Viking
12:16 AM GMT on June 03, 2008
678. IKE 12:10 AM GMT on June 03, 2008

When did you move to South Central Mexico!?
Member Since: August 25, 2006 Posts: 1 Comments: 3022
683. dearmas
12:16 AM GMT on June 03, 2008
Hi all. How's everyone doing?
Member Since: August 23, 2006 Posts: 0 Comments: 121
682. MasterForecaster
12:15 AM GMT on June 03, 2008
Good evening CCHS, Everyone...

Looks like these are two circulations that do NOT want to die...does anyone know whats going on with the other waves?

Also...I've discovered how to prevent Hurricanes from striking the land, if anyone cares to ask...
681. weatherblog
12:15 AM GMT on June 03, 2008
If 91E develops... Arthur's remnants will most likely not form into Bertha due to Boris's remnants moving into the general direction of the BOC also, but then those remnants can form into something also. So, I think during the next couple of days timing is everything which is normally the situation in the tropics.
Member Since: July 10, 2006 Posts: 27 Comments: 1623
679. weatherblog
12:11 AM GMT on June 03, 2008
*675

You're welcome, condesa...! Wunderground is great for anybody interested in weather; that is, unless you meet a 'stormy' on the blogs, but that's a whole different story.
Member Since: July 10, 2006 Posts: 27 Comments: 1623
678. IKE
12:10 AM GMT on June 03, 2008
675. condesa 7:07 PM CDT on June 02, 2008
Ok, WeatherBlog. Thanks.
I am in south central Mexico; it's hard to keep track or know what's really developing or happening. I really appreciate Wunderground, more than ever.


Same here.........
Member Since: June 9, 2005 Posts: 23 Comments: 37858
677. cchsweatherman
12:08 AM GMT on June 03, 2008


There is an upper-level anticyclone over between Arthur's remnant low and 91E. If the anticyclone moves north, Arthur will have a real chance for re-development into Bertha.
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676. GeoffreyWPB
12:08 AM GMT on June 03, 2008
Where is it??? Where is it??? Okay, found it....Let's see....Apply directly to the forehead...Much better now.
Member Since: September 10, 2007 Posts: 0 Comments: 11149
675. condesa
12:07 AM GMT on June 03, 2008
Ok, WeatherBlog. Thanks.
I am in south central Mexico; it's hard to keep track or know what's really developing or happening. I really appreciate Wunderground, more than ever.
674. moonlightcowboy
12:06 AM GMT on June 03, 2008
Evil Twins visible loop
Member Since: July 9, 2006 Posts: 184 Comments: 29610
673. weatherblog
12:06 AM GMT on June 03, 2008
cchs...IF it were to re-develop, the interesting thing it would be named Bertha, not Arthur. But, then again, has anyone even looked at shear in the BOC or the amount dust present for the next 24-36 hours?
Member Since: July 10, 2006 Posts: 27 Comments: 1623
672. 69Viking
12:06 AM GMT on June 03, 2008
668. cchsweatherman 12:01 AM GMT on June 03, 2008

Look JP, somebody else think what the weatherblog thought.
Member Since: August 25, 2006 Posts: 1 Comments: 3022
671. 69Viking
12:04 AM GMT on June 03, 2008
658. jphurricane2006 11:53 PM GMT on June 02, 2008

A few of us have said it could. The NHC isn't god you know. Come on, this system has maintained a circulation over land and is headed for 84 degree water. What about this year has been normal btw and followed what the Hurricane Center has predicted? The point is everyone can have their opinion and I'll second the thought that the remnants of Arthur have a good chance to reform if it gets back over warm water.
Member Since: August 25, 2006 Posts: 1 Comments: 3022
670. cchsweatherman
12:03 AM GMT on June 03, 2008
Arthur's remnant low may be slightly stronger than 91E according to the CIMSS 850mb Vorticity Map.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
668. cchsweatherman
12:01 AM GMT on June 03, 2008


Looks like the remnant low from Arthur will be entering the Bay of Campeche overnight with diurnal maximum occuring. Appears that the chances may be increasing for re-development with the low as strong convection has now covered the low. If 91E does not deepen and strengthen, we may see Arthur's remnant low win the battle.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
667. IKE
12:00 AM GMT on June 03, 2008
665. weatherblog 6:57 PM CDT on June 02, 2008
weatherblog, #1 isnt really true

no one said; well at least the NHC didnt say that development was possible even if the remnants of Arthur got into the BOC

That's what I've been hearing on the blogs though. lol



It could happen....odds not great...but, nothing is written in stone.......that's why we watch.......
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666. moonlightcowboy
11:58 PM GMT on June 02, 2008
659. Thank you, Drak. Just think about us if you see sumpin' bad! :)
Member Since: July 9, 2006 Posts: 184 Comments: 29610
665. weatherblog
11:57 PM GMT on June 02, 2008
weatherblog, #1 isnt really true

no one said; well at least the NHC didnt say that development was possible even if the remnants of Arthur got into the BOC


That's what I've been hearing on the blogs though. lol
Member Since: July 10, 2006 Posts: 27 Comments: 1623
664. presslord
11:57 PM GMT on June 02, 2008
sorry sj...it's my only vice...yup...looks like things are wakin' up....
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663. 69Viking
11:55 PM GMT on June 02, 2008
656. IKE 11:53 PM GMT on June 02, 2008

I'll second that!
Member Since: August 25, 2006 Posts: 1 Comments: 3022
662. IKE
11:55 PM GMT on June 02, 2008
660....yo bud.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
661. StormJunkie
11:55 PM GMT on June 02, 2008
654. lol

I caught hell for that pet pevee this weekend press.

Models still showing the Atl showing signs of life over the next week?
Member Since: August 17, 2005 Posts: 26 Comments: 16505
660. tornadofan
11:54 PM GMT on June 02, 2008
656 - IKE - that must mean their human. Okay.

655 - tunnels.
Member Since: April 5, 2007 Posts: 83 Comments: 12345
659. Drakoen
11:54 PM GMT on June 02, 2008
653. moonlightcowboy 11:51 PM GMT on June 02, 2008
650. LOL. ......ain't it fun negotiating! ;)


Its hard to say no to ya MLC! LOL.
Member Since: October 28, 2006 Posts: 57 Comments: 30489
657. 69Viking
11:53 PM GMT on June 02, 2008
652. weatherblog 11:51 PM GMT on June 02, 2008

Some of the most accurate straight talk I've heard all day!
Member Since: August 25, 2006 Posts: 1 Comments: 3022

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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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