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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You should probably ignore him until he takes the picture of his wife off his avatar.
A little higher heights? Negative-ish NAO possibly.
relax that is not JFV
PREDICT pouch synopsis for PGI31L
I am an advanced spotter also. As Storm said, it's all volunteer...though I guess you could make a job out of it if you had enough severe weather and are a great photographer.
That's possible too if it sits there for a little while to be in line with the model predictions. The GFS seems to develop that pouch while the ECMWF isn't as clear-cut. ECMWF might be seeing a merging with the wave behind.
KT. GLOBAL MODEL GUIDANCE AND POTENTIAL VORTICITY FIELDS
INDICATE THAT THE SOUTHERN EXTENT OF THE WAVE IS EMBEDDED WITHIN
A BROAD MONSOONAL TROUGH ACROSS THE TROPICAL ATLC S OF 16N
BETWEEN 21W-36W. THE WAVE ALSO COINCIDES WITH A MAXIMUM IN DEEP
LAYER MOISTURE INDICATED BY TOTAL PRECIPITABLE WATER IMAGERY E
OF 31W. AFRICAN DUST IS NOTED BEHIND THE WAVE AXIS FROM 17N-28N.
DUE TO THIS AREA OF DRIER AIR...NO SIGNIFICANT AREAS OF DEEP
CONVECTION ARE CURRENTLY ASSOCIATED WITH THE WAVE.
TROPICAL WAVE EXTENDS FROM 23N34W TO 10N40W MOVING W AT 10-15
KT. BROAD LOW-LEVEL CYCLONIC FLOW IS NOTED IN THE VICINITY OF
THE WAVE WITH A LARGE SURGE OF DEEP LAYER MOISTURE LOCATED TO
THE EAST AND REMAINING LARGELY ASSOCIATED WITH THE PREVIOUS
TROPICAL WAVE. THE SIGNIFICANT DRY AIR TO THE EAST IS
SUPPRESSING CONVECTION NEAR THE WAVE AND LIMITING IT TO THE ITCZ
REGION S OF 11N.
Well no not from the one immediately behind PGI31L. There appear to be two different waves over western Africa with a 2nd one back over Nigeria. That one could potentially be another storm later on, but the one over western Africa that will be emerging in about 24 hours will probably merge somehow with the energy out in front that is stalling a little bit.
Wonder how much training it would take to accurately determine that this road is completely submerged underwater? LOL
what? I am not one of the "sane" ones here?
ROFL!
I know I just pop in Dr Master's blog every now and then until we have something to watch.
So I am leaving this weekend Friday morning and returning Monday afternoon... hoping my home in Ft Lauderdale is not under any type of "threat" while I am gone. lol
really I now think we will be just fine leaving our home and our very loved Harley this weekend..without anything coming this way...
Have a great Tuesday!
Gams/aka Gamma
The Quasi-Biennial Oscillation is associated with a type of gravity wave that is theorized can affect hurricane activity in the deep tropical Atlantic, but the QBO has little correlation during a warm AMO, which may be enough to offset it.
It was a joke. Sarcasm towards me for no reason. How typical.
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