Weather456's Tropical Weather Blog

Tropical Weather Review Week Ending 10 Jan 2009

By: Weather456, 7:11 PM GMT on January 11, 2009

Tropical Weather Review for Week ending 10 Jan 2009

....SPECIAL FEATURES OF INTEREST....

NONE

....UPPER LEVELS....

THE FLAT ZONAL PATTERN DISPLAYED LAST WEEK BECAME MORE WAVE-LIKE WITH UPPER ANTICYCLONIC FLOW AROUND THE CREST OF AN ANTICYCLONE OVER THE CARIBBEAN THRU SUN-TUE...DEVIATING TO CYCLONIC THEREAFTER AS A MID-LATITUDE TROUGH SWUNG ACROSS THE GULF AND WESTERN ATLANTIC REGION THRU WED-FRI. UPPER RIDGING RETURNED TO THE AREA ON SAT.

UPPER ANTICYCLONE DOMINATED THE CARIBBEAN CENTERED OVER THE WEST WITH CONFLUENT FLOW DOMINATING THE EASTERN FLANK...EAST OF 70W. THIS PATTERN LASTED THRU THU WITH THE UPPER ANTICYCLONE BECOMING LESS DEFINED UNTIL FLAT RIDGING TOOK OVER.

AN UPPER TROUGH DEVELOPED AND AMPLIFIED ACROSS THE TROPICAL ATLANTIC FROM TUE...BETWEEN 60W AND 30W WHILE REACHING AS FAR SOUTH AS 9N. MEANWHILE, AN UPPER LEVEL LOW PRESSURE AREA DEVELOPED WITHIN THE TROUGH ON FRI NEAR 22N-39W AND MOVED TOWARDS THE SOUTHWEST ALONG 21N-41W.

THE EXACT FORMATION OF THE TROUGH CAN BE ATTRIBUTED TO THE OTHER UPPER TROUGH THAT PUSHED OFF THE UNITED STATES WHICH CAUSED AN UPPER RIDGE TO BE PUSHED EASTWARD INTO THE SUBTROPICAL ATLANTIC, ADJACENT TO ANOTHER UPPER RIDGE NEAR THE AFRICAN COAST. THE HORIZONTAL SHEAR VORTICITY THAT DEVELOPED BETWEEN THE TWO FEATURES CAUSED AN UPPER TROUGH TO FORM RE-ENFORCED BY AN EVEN LARGER UPPER TROUGH OVER SOUTHERN EUROPE.

....SYNOPTIC FEATURES....

THE ASSOCIATED SURFACE COLD FRONT PUSHED ACROSS THE SOUTHERN UNITED STATES AND GULF OF MEXICO FROM SUN THRU WED...ENTERING THE ATLANTIC AND NORTHWESTERN CARIBBEAN SEA THRU THU. THE PORTION OF THE FRONT SOUTH OF CUBA LOST IT DISCONTINUITY AND WEAKEN TO A SHEAR LINE THRU FRI, WHILE THE NORTHERN PORTION CONTINUED TO TRACK ACROSS THE WESTERN/CENTRAL ATLANTIC. HIGH PRESSURE THEN TOOK OVER IN THE WAKE OF THE FRONTAL PASSAGE.

OVER THE CARIBBEAN...A TYPICAL PRESSURE PATTERN DOMINATED WITH A SERIES OF SURFACE TROUGHS DEVELOPING ACROSS THE CENTRAL CARIBBEAN FROM SUN TO TUE. A COLD FRONT ENTERED THE NORTHWEST REGION ON THU, BECAME STATIONARY AND DISSIPATED INTO A SHEAR LINE BY FRI.

CONTINUING FROM LAST WEEK...MID-LATITUDE COLD FRONTS BETWEEN 75W AND 40W, NORTH OF 30N DISSIPATED AND/OR PUSHED INTO THE NORTHERN ATLANTIC CAUSING TWO HIGH PRESSURE CENTERS (THE MIGRATORY WEST ATLANTIC AND THE SEMI-PERMANENT AZORES) TO MERGE THRU TUE AND STRENGTHEN THRU FRI. THE WELL-DEFINE COLD FRONT FROM THE WEST BEGAN TO ENTER THE SUBTROPICAL ATLANTIC THRU SAT.

THE AVERAGE LOCATION OF THE ITCZ WAS ALONG 0N WEST OF 40W, INCREASING TO 5N EAST OF THERE. THE NORTHERN MOST-POSITION LIED NEAR 5N ALONG THE AFRICAN COAST FOR MOST OF THE WEEK AND NEAR THE EQUATOR ALONG SOUTH AMERICA.

....SIGNIFICANT CLOUDINESS, CONVECTION AND RAINFALL.....

A AN EXTENSIVE BAND OF OVERCAST MULTILAYER CLOUDINESS WITH EMBEDDED SCATTERED SHOWERS EXTENDED FROM THE EASTERN PACIFIC OCEAN ACROSS NORTHERN MEXICO INTO THE SOUTHERN UNITED STATES THRU TUE CAUSED BY THE SOUTHWESTERLY FLOW AHEAD OF AN UPPER TROUGH OVER THE WESTERN UNITED STATES. AS THIS TROUGH EVOLVED EASTWARD, THE BAND NARROWED AND CONCENTRATED ALONG THE ASSOCIATED FRONTAL BOUNDARY WHICH MOVED ACROSS THE GULF OF MEXICO THROUGH WED. MID-UPPER LEVEL CLOUDS WAS ADVECTED BY THE UPPER RIDGE OVER THE CARIBBEAN WHICH SUPERIMPOSED THE LOW LEVEL CLOUDINESS ALONG THE FRONT. THIS PATTERN CONTINUED THRU FRI IN THE WESTERN ATLANTIC BUT THE UPPER LEVEL CLOUDINESS WAS A RESULT OF THE DIVERGENCE AHEAD OF UPPER TROUGH INSTEAD.

SIGNIFICANT CLOUDINESS OVER THE CARIBBEAN LAID MAINLY IN THE NORTHWEST WHERE MULTILAYER CLOUDINESS FROM THE SURFACE FRONT AND THE FLOW BETWEEN THE UPPER RIDGE AND TROUGH EVADED THE AREA ON THU THRU FRI. THE CLOUDINESS DISSIPATED ALONG WITH THE FRONTAL FEATURES. MEANWHILE, A SURGE OF EASTERLY TRADES BROUGHT PATCHES OF LOW LEVEL CLOUDINESS AND MOISTURE INTO THE CARIBBEAN ON SAT WITH ADDITIONAL MID-UPPER LEVEL CLOUDINESS DEVELOPING OVER CENTRAL AMERICA ON THE WESTERN FLANK OF THE RIDGE.

EARLY IN THE WEEK CLOUDINESS DOMINATED THE SUBTROPICAL ATLANTIC FROM 70W TO 40W BETWEEN 20N AND 30N AS THE PREVIOUS WEEK’S FRONTAL SYSTEMS MOVED OUT. WIDESPREAD CLOUDINESS DEVELOPED OVER THE CENTRAL/EASTERN TROPICAL ATLANTIC FROM WED AS THE UPPER TROUGH AMPLIFIED. THIS BAND OF CLOUDINESS EXTENDED FROM THE ITCZ TO 35N, EAST OF 40W THRU FRI. ON SAT, THE BAND SHIFTED NORTH OF 10N AND BECAME ITS MOST INTENSE.

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Tropical Weather Review for Week Ending 03 Jan 2009

....SPECIAL FEATURES OF INTEREST....

NONE

....UPPER LEVELS....

UPPER LEVEL RIDGING DOMINATED THE GULF OF MEXICO IN THE EARLY PART OF THE WEEK BUT GRADUALLY GAVE WAY TO WESTERLY ZONAL FLOW THAT DOMINATED OVER THE REGION AND WELL INTO THE NORTHWESTERN ATLANTIC FOR MUCH OF THE WEEK.

PERSISTENT UPPER RIDGING DOMINATED THE CARIBBEAN BASIN AND CENTRAL AMERICA FOR THE ENTIRE WEEK AND PARTS OF THE BAY OF CAMPECHE LATE IN THE WEEK...CENTERED ON A UPPER HIGH OVER SOUTH AMERICA IN THE FIRST HALF OF THE WEEK AND OVER THE PACIFIC OCEAN/SW CARIBBEAN OVER THE SECOND HALF.

OVER THE TROPICAL ATLANTIC, A WEAK TROUGH-LIKE PATTERN EXISTED FOR THE EARLIER PART OF THE WEEK BUT SIMILARLY TO THE WESTERN ATLANTIC, THE PATTERN BECAME MORE FLAT AND ZONAL AS THE WEEK PROGRESSED.

....SYNOPTIC FEATURES....

AS THE WEEK STARTED, A COLD FRONT WAS PUSHING ACROSS THE SOUTHERN UNITED STATES AND ACROSS THE GULF. BY MID-WEEK, THE SOUTHERN PORTION OF THE FRONT BECAME STATIONARY AND DISINTEGRATED INTO AN OPEN TROUGH OVER THE GULF, WHILE THE NORTHERN HALF CONTINUED TO PUSH ACROSS THE ATLANTIC. ANOTHER COLD FRONT QUICKLY SUCCEEDED AND PUSHED ACROSS THE GULF AND THE ATLANTIC OCEAN IN THE LATTER PART OF THE WEEK. THIS SERIES OF FRONTS GAVE WAY TO SPRAWLING HIGH PRESSURE WHICH BRIEFLY DOMINATED THE REGION WITH A STABLE ATMOSPHERE AND 10-20 KNOT ANTICYCLONIC FLOW.

MUCH OF THE CARIBBEAN REMAINED IN THE PERSISTENT FLOW OF THE EASTERLY TRADES SOUTH OF THE SUBTROPICAL RIDGE WHICH WAS OCCASIONALLY INTERRUPTED BY PASSING FRONTAL BOUNDARIES NORTH OF THE REGION.

THE AVERAGE LOCATION OF THE ITCZ WAS 5N WEST OF 30W AND 6-7N EAST OF 30W. THE NORTHERN MOST POSITION OCCURRED 06/29 AT 10N INDUCED BY A SURFACE TROUGH. THE SOUTHERN-MOST POSITION WAS AT 0N 06/31 NEAR THE MOUTH OF THE AMAZON ALONG THE SOUTH AMERICAN COAST.

....SIGNIFICANT CLOUDINESS, CONVECTION AND RAINFALL.....

MID-UPPER LEVEL CLOUDINESS/SHOWERS OCCURRED ALONG THE NORTHERN GULF COAST WHERE UPPER LEVEL WINDS CONTINUOUSLY ADVECTED MOISTURE ACROSS THE AREA FROM THE EASTERN PACIFIC.

BROKEN TO OVERCAST PATCHES OF COLD AIR STRATOCUMULUS DOMINATED MUCH OF THE WESTERN ATLANTIC BEHIND A NUMBER OF COLD FRONTS.
MUCH OF THE CARIBBEAN REMAINED HIGH AND DRY WITH PATCHES OF LOW LEVEL CLOUDS BEING CONTINUOUSLY ADVECTED INTO THE REGION BY THE NORTHEASTERLY TRADES.

THE WEAK UPPER TROUGHING IN THE EARLY PART OF THE WEAK INTERACTED WITH THE ITCZ TO PRODUCE A BAND OF CLOUDINESS AND SHOWERS WHICH EXTENDED ACROSS THE TROPICAL ATLANTIC. THE AREA GRADUALLY DIED DOWN BUT SHOWERS STILL PERSISTED ACROSS THE ATLANTIC ESPECIALLY ALONG THE SOUTH AMERICAN COAST.

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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.