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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NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT WED AUG 18 2010
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
CLOUDINESS AND SHOWERS OVER THE WEST CENTRAL CARIBBEAN ARE
ASSOCIATED WITH A TROPICAL WAVE MOVING WESTWARD AT 15 MPH. THERE
ARE NO SIGNS OF DEVELOPMENT AND THERE IS A LOW CHANCE...10
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER CANGIALOSI/KIMBERLAIN
Yeah; and I forgot to mention the Greater Antilles.........
Fort Polk, Base Reflectivity 0.50 Degree Elevation Range 248 NMI
Wow storm! The SAL has diminished pretty fast since Monday.
NEXRAD Radar
Fort Polk, Storm Total Surface Rainfall Accumulation Range 124 NMI
Prayer up too,,and maybe the Calamity will come.
Good Luck.
Im going fishing.
Ciao..!
Textbook, indeed...
Thanks for posting the Louisiana radar throughout the day Pat. Im at work and can't ever look at it because they have alot of websites blocked! ;[
Shhhh. You might anger the fishcasters. Don't want to put ripples in the water.
Well today itsa gonna be hard to as we going to Black Bay fer some relaxation and Beer Invests..
If da neighbor can find his Tackle box.
LOL
C-yas
well, I see that the soap "As the Storm Turns" is being written for the CV system. Wonder how many times the storyline will change before the episode ends?..lol
We have Dunkin Donuts on every street corner here in Southern New England.
LOL. Very funny.
East Coast landfalling hurricanes, except those forming during a warm phase, typically form farther east than those that strike Florida or the Gulf Coast (Figs. 5 –7). In fact, the median longitude of tropical storm classification during cold and neutral ENSO phases is near or less than the 25th percentile longitude for both Florida and Gulf Coast landfalling hurricanes (Fig. 7). Tropical cyclones that form in the far eastern Atlantic have more time to be influenced by upper-level troughs as they travel across the Atlantic, thereby increasing the likelihood that they will reach a more northern latitude and impact the East Coast. During the ENSO cold phase, the 19.0° difference in median longitude of tropical storm classification between hurricanes making East Coast versus Florida landfall is significant at the 99% level.
Well, here in Haiti I haven't seen one on any corner. Lol
Reference?
06Z GFS sure is responding to that negative NAO and sure quite resembles storm's steering pattern of the almost textbook NAO setup w/ the A/B high.
On the other hand ECMWF not quite picking up on this, but on thing is for sure... NOGAPS and CMC are definitely on board with development. Can't blame them based on:
Little dust to worry about:
From an AMS journal article I believe; have the text saved on my hardrive but you can google the artice and get the authors....
What's up Jason? Kit still in the head this morning. LOL I heard em all night long
Let me guess, they turned it into yet another Waffle House...
Reviewing the ECMWF I think what happens is the wave south of the Cape Verde islands and the wave you mentioned will combine (remember Colin's genesis?) to create a system.
Category 3 hurricane by 240 hours.
I looked it up for you; here it is:
Smith, Shawn R., Justin Brolley, James J. O’Brien, Carissa A. Tartaglione, 2007: ENSO’s Impact on Regional U.S. Hurricane Activity. J. Climate, 20, 1404-1414 doi: 10.1175/JCLI4063.1
ENSO’s Impact on Regional U.S. Hurricane Activity
Shawn R. Smith, Justin Brolley, James J. O’Brien, and Carissa A. Tartaglione
Center for Ocean–Atmospheric Prediction Studies, The Florida State University, Tallahassee, Florida
HOT HOT HOT -
presently 78 degrees/93% humidity - taking the dog out for the long walk now - before the roads heat up
Don't want a HOT DOG
My suburban chickens have not laid eggs for two days
I think w/this heat their worried they'll come out hard boiled
Of the 4 models I look at...the ECMWF, CMC, and NOGAPS....have a track north, in longitude, of the islands and looks possibly headed out to sea.
Only the GFS has it hitting the islands and even that model curves it east of the USA.
Encouraging news possible on the NAO from the latest ECMWF...
AND....the GFS is pointing to another low for early next week in the northern gulf.
Thanx for remembering that we're here. Especially Puerto Rico and Dominican Republic. It's been a while since the last hurrican hit us, and, unfortunately, it looks like we're due for another big one.
I love the strawberry ones.
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