An active Atlantic hurricane period coming
The remnants of Tropical Depression Five are no longer a threat, done in by high wind shear and close proximity to land. However, an active period for Atlantic hurricanes is likely for the remainder of August, as the global atmosphere undergoes a major change to the circulation pattern that has dominated Northern Hemisphere weather during July and August. A large trough of low pressure is gathering strength over Europe, and is expected to push eastward. By Thursday, this trough should be able to push away the blocking ridge of high pressure that has given Russia its worst heat wave in history. The shift in circulation has already weakened the large region of sinking air that has brought dry, stable conditions to the tropical Atlantic over the past month. Vertical instability, which was unusually low since late July, has now returned to near normal levels over the tropical Atlantic (Figure 1), though it remains quite low over the rest of the North Atlantic. Instability is measured as the difference in temperature between the surface and the top of the troposphere (the highest altitude that thunderstorm tops can penetrate to.) If the surface is very warm and the top of the troposphere is cold, an unstable atmosphere results, which helps to enhance thunderstorm updrafts and promotes hurricane development. Since SSTs in the Atlantic were at record highs and upper tropospheric temperatures were several degrees cooler than average in July, enhancing instability, something else must have been going on to reduce instability. Dry air can act to reduce instability, and it appears that an unusually dry atmosphere, due to large-scale sinking over the Atlantic, was responsible for the lack of instability. Now that vertical instability has returned to near normal levels, Atlantic hurricane activity should increase to at least average levels over the next two weeks. This is particularly true since SSTs are at record highs and vertical wind shear is at average to below average levels over the tropical Atlantic.
Figure 1. Vertical instability (in °C) over the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right) in 2010. Normal instability is the black line, and this year's instability levels are in blue. The atmosphere became much more stable than normal in both regions at the end of July. This lack of instability also extended to the Gulf of Mexico and North Atlantic Ocean between Europe and North America. However, in the past few days, vertical instability has returned to normal, thanks to a major pattern shift in the global atmosphere. Image credit: NOAA/CIRA.
Figure 2. The climatology of Atlantic hurricane activity shows a sharp rise in activity around August 18.
Analysis
August 18 historically marks the point where Atlantic hurricane activity makes a major spike upwards (Figure 2.) On average, we can expect to see two named storms and one hurricane during the last half of August. The last half of August usually sees a moistening of the atmosphere off the coast of Africa, as the the African monsoon kicks into high gear. This year is no exception (Figure 3.) The dry Saharan Air Layer (SAL) has retreated to the north, leaving a moist atmosphere conducive for tropical cyclone development off the coast of Africa.
It would not be a surprise to see atmospheric instability increase to above-average levels by early next week as the major atmospheric pattern shift progresses. Will this usher in a hyperactive period of Atlantic hurricane activity next week, with a parade of three or four simultaneous storms strung out across the Atlantic? Probably not, since the Madden-Julian Oscillation (MJO) only marginally favors upward motion over the tropical Atlantic, and is not forecast to change much over the next ten days. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The bottom line: I expect we will see 2 - 3 named storms in the Atlantic by the end of August, including one hurricane. Where these storms might develop and move is difficult to say. It currently appears that the global shift in circulation will bring near-average steering currents to the Atlantic over the next ten days, with a series of troughs of low pressure capable of recurving hurricanes, moving across the Atlantic. The GFS model is indicating, though, that during the few days of August, these troughs may weaken, making recurvature of hurricanes less likely, and increasing the probability of landfalling storms.
The GFS, NOGAPS, and ECMWF currently predict that one or two tropical storms will form between Africa and the Lesser Antilles Islands during the period 4 - 10 days from now. The NOGAPS model is predicting the development of a strong tropical disturbance near the coast of Honduras late this week.
Figure 3. Saharan Air Layer (SAL) analysis shows that the dry air and dust of the SAL (orange colors) lies well to the north of the hurricane breeding grounds off the coast of Africa, near the Cape Verdes Islands. Image credit: University of Wisconsin/NOAA Hurricane Research Division.
Smoke bedeviling Moscow again
Light easterly winds over the past few hours have brought smoke from wildfires back into Moscow today. Temperatures at Moscow's Domodedovo airport hit 29°C (84°F) today, which is 11°C (20°F) above average. The latest forecast for Moscow predicts that just one more day remains for Russia's greatest heat wave in recorded history. On Thursday, a strong trough of low pressure will move through European Russia, finally bringing below average temperatures.
Jeff Masters
Reader Comments
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typo - meant live here - but same difference
I don't really think there is anything wrong with typing in Spanish on here...it's just frustrating for the vast majority of the people on the site reading the blog because they can't understand it, that's all. And obviously there are other issues beneath the surface that some people have problems with that I'm not going to go into, and that I am not part of.
I'm in Ohio so this whole Spanish/English thing is not really an issue here...lol very few speak Spanish!
It seems to me that in a blog about tropical weather that's focused on the Caribbean Sea and the Gulf of Mexico, posts in Spanish or even Creole should be ok.
I can't read Spanish, but I consider posting in it no more rude than the references to sports teams I don't care about, or the chitchat between oldtimers who I don't know anything about.
To drag this back on topic a little, I'm trying to do more this year to prepare for emergencies at home. I wonder if some of the more savvy readers here could recommend some good starter sources of information. I already know about FEMA's site, and the Red Cross. Are there other resources you think are particularly good? Thanks!
Tormentoso83: on the internet, typing in all capitals is considered the same as shouting. It's not good manners; it makes you sound rude.
Second door on the right :o)
There are many bloggers/lurkers living in hurricane/typhoon prone Hispanic, French, Hindi, Japanese, Tagalo and many other language areas. Hopefully this site will continue to be tolerant enough to give information to all who don't speak English, because it really comes down getting info worldwide on life-threatening situations in our great worldwide community. Is it really a big deal to have a comment or two in various languages? I find it fun and enriching to learn new wx-words, maybe even in Hindi or "Australian (soz Aussie bros:) lmao...
Posts in in different languages makes this a wonderful international website. Momentary bursts of ego and taking offense are ok, that's human nature. Hatred is a poison that only hurts us all in the long run.
PS. I'll gladly translate any comments anybody can't understand, just WUmail me :)
;)
Hello, this arguing about language is senseless. It is good for people to communicate. Hurricanes and all weather affect everyone.
It would help if the folks sharing in a foreign language could help with a lil' English sub-titles!!
you are right, sorry about that I didn't notice before because I was reffering to people that may not deserves respect from me because they disrespected me!!!
You mean "baño"? Yes, I have a Spanish keyboard LOL!
ECMWF 00z still recurves the storm.
El ECMWF de las 00z aún recurva la tormenta.
Maybe those who write in Spanish should make a short translation.
Amen.
I apologize
The blog police
Police! Police!"
;)
Peas, peas, peas, peas....
Eating goober peas!
I'm not sure if links are allowed but...
http://translate.google.ca/?hl=en&tab=wT#auto|en|
"I surrender"
Now back to the weather.....
Here ya go :) Sometimes the www.onestorm.org server is busy, keep trying...
Patrap has good info too and IMA's blog is great if you have pets.
Hasta mañana everybody, thanks for great graphics and info.
Completely racist and inappropriate. Flagged and reported.
Additionally, consider that Dr. Masters has not stated that this is an English-only blog, and that many of our blogging friends in the Caribbean are Spanish-speaking, and come here for life-saving information about tropical events that may affect their islands.
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