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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There's probably a cirrus cloud over the Indian Ocean that needs a pouch designation.
Nah, the storms to the east between Houston and Beaumont look to be pushing south.
CENTRAL WEST FELICIANA...WEST BATON ROUGE...EAST BATON ROUGE...WEST
CENTRAL LIVINGSTON...SOUTHWESTERN EAST FELICIANA AND SOUTHEASTERN
POINTE COUPEE PARISHES...
AT 544 PM CDT...TRAINED WEATHER SPOTTERS REPORTED WATER COVERING
SOME ROADS IN THE NEW ROADS AREA...WITH MANY OF THE SIDE DITCHES
FULL. HEAVY RAINFALL CONTINUES TO IMPACT MUCH OF SOUTH CENTRAL
LOUISIANA...AND THE THREAT FOR FLASH FLOODING CONTINUES.
LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO ZACHARY...ST.
FRANCISVILLE...SLAUGHTER...NEW ROADS...MORGANZA AND BAKER
ADDITIONAL RAINFALL AMOUNTS OF ONE TO THREE ARE POSSIBLE IN THE WARNED AREA...WHERE TWO TO FOUR INCHES OF RAINFALL HAVE ALREADY FALLEN. EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL CREEKS AND STREAMS...URBAN AREAS...HIGHWAYS...STREETS AND UNDERPASSES AS WELL AS OTHER DRAINAGE AREAS AND LOW LYING SPOTS. A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING. IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY. RESIDENTS LIVING ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE PRECAUTIONS TO PROTECT LIFE AND PROPERTY. DO NOT ATTEMPT TO CROSS SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN DEPTH BY FOOT OR BY AUTOMOBILE
Please start using Deported instead of Reported. It's so much better of a description of what should happen around this blog. Makes me laugh as well.
Hey Buddy, where did that come from? Cayman , don't see any storms headed here, maybe some rain the TW around Haiti/DR. Which model shows anything coming around the Caymans, seen one showing the EAst coast, possibly Georgia???
...and tattled on to boot!
lol
Thanks Taz. Awesome. Love me some Tazbonics.
Of course the models use Newton's Laws. They're just highly non-linear and chaotic. In theory you can know the physics of the hurricane precisely, but do to the non-linearities, the path will still be uncertain. Their highly sensitive to initial conditions.
I don't really understand your second question. Are you talking in the context of fluid flow? If a solid body by different force all pointing in the same direction, it would create a torque and spin the object, not curve it. In terms of a solid passing through a fluid, if the fluid had viscosity, a spinning object would curve the object.
Link
I second this motion.
You know what even sadder? Grown men reporting on grown men shouting.
Bahahaha!!
ABNT20 KNHC 172346
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT TUE AUG 17 2010
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
A TROPICAL WAVE LOCATED OVER EASTERN HISPANIOLA AND EXTENDING
SOUTHWARD OVER THE CENTRAL CARIBBEAN SEA IS PRODUCING WIDESPREAD
CLOUDINESS AND DISORGANIZED SHOWER ACTIVITY. DEVELOPMENT OF THIS
DISTURBANCE...IF ANY...SHOULD TO BE SLOW TO OCCUR OVER THE NEXT
COUPLE OF DAYS DUE TO UNFAVORABLE ENVIRONMENTAL CONDITIONS. THERE
IS A LOW CHANCE...10 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES GENERALLY WESTWARD
AT 15 TO 20 MPH.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER STEWART
LOL!
105 to go...and it's over. Unless.
hey i lost that cloud yeasterday thanks
you know thats a pure breed show cloud
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