Tropical Storm Aletta

[*Stormforce~beka*]

And here we have her - First of the season! ...

000

WTPZ31 KNHC 280809

TCPEP1

BULLETIN

TROPICAL STORM ALETTA ADVISORY NUMBER 5

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP012006

200 AM PDT SUN MAY 28 2006

...ALETTA MEANDERING WELL OFFSHORE THE SOUTH-CENTRAL MEXICAN COAST...

A TROPICAL STORM WARNING IS IN EFFECT FOR THE SOUTH-CENTRAL PACIFIC

COAST OF MEXICO FROM PUNTA MALDONADO WESTWARD TO TECPAN DE GALEANA.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE

EXPECTED WITHIN THE WARNING AREA WITHIN THE NEXT 24 HOURS.

A TROPICAL STORM WATCH IS IN EFFECT FOR THE PACIFIC COAST OF MEXICO

FROM EAST OF PUNTA MALDONADO EASTWARD TO PUERTO ESCONDIDO...AND FROM

WEST OF TECPAN DE GALEANA WESTWARD TO ZIHUATANEJO.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE

POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE

INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED

BY YOUR LOCAL WEATHER OFFICE.

AT 200 AM PDT...0900Z...THE CENTER OF TROPICAL STORM ALETTA WAS

LOCATED NEAR LATITUDE 15.4 NORTH...LONGITUDE 101.0 WEST OR ABOUT 125

MILES...205 KM...SOUTHWEST OF ACAPULCO MEXICO.

ALETTA HAS ESSENTIALLY BEEN STATIONARY THIS MORNING...AND SOME

ERRATIC MOTION IS POSSIBLE. HOWEVER...A SLOW NORTHWARD OR

NORTH-NORTHEASTWARD MOTION IS EXPECTED TO BEGIN LATER THIS

AFTERNOON. THE CENTER MAY APPROACH THE COAST OF MEXICO BY SUNDAY

NIGHT OR EARLY MONDAY IF THE NORTHWARD MOTION DEVELOPS.

MAXIMUM SUSTAINED WINDS ARE NEAR 45 MPH...75 KM/HR...WITH HIGHER

GUSTS. SOME SLOW STRENGTHENING IS POSSIBLE DURING THE NEXT 24

HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 60 MILES...95 KM..

MAINLY EAST OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB...29.59 INCHES.

ALTHOUGH RAIN BANDS ASSOCIATED WITH ALETTA HAVE STOPPED MOVING

ONSHORE THE MEXICAN COAST THIS MORNING...ADDITIONAL RAIN BANDS MAY

REDEVELOP LATER TODAY AND PRODUCE RAINFALL AMOUNTS OF 1 TO 3

INCHES...WITH LOCALLY HIGHER AMOUNTS OVER MOUNTAINOUS TERRAIN.

REPEATING THE 200 AM PDT POSITION...15.4 N...101.0 W. MOVEMENT...

STATIONARY. MAXIMUM SUSTAINED WINDS...45 MPH. MINIMUM CENTRAL

PRESSURE...1002 MB.

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE

CENTER AT 500 AM PDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 800

AM PDT.

FORECASTER STEWART

$$

[Mondy]

[Mondy]

Firing off convection quite nicely:

[wolves78]

TROPICAL STORM ALETTA NEAR 15.4N 101.0W AT 0900 UTC. ALETTA IS

NEARLY STATIONARY. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002

MB. MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT.

SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS

MIATCMEP1/WTPZ21 KNHC FOR MORE DETAILS. THE STORM HAS BEEN

MAINTAINING A BALL OF CONVECTION ON IT'S E SIDE WITH VERY COLD

TOPS. THERE IS EVIDENCE OF AN ANTICYCLONIC FLOW PATTERN ABOVE

THE STORM WHICH IS CONDUCING TO MAINTAINING STRONG CONVECTION

[kold weather]

He we go again then, this time of year I love most!

My first point of note is I don't think the track forecast is takng the system far enough eastwards before pushing it back out to sea, granted its early days but I think the GFDL model is far more likely to be correct then the NHC, who favor the sub-tropical ridge to stay still fairly strong to the east of Aletta and cause it to push north-wards rather then eastwards like GFDL suggests.

As the offical discussion states the center seems to have drifted away from the convection a little, as you can clearly see from the image a few posts ago. However the center hasn't been exposed and thanks a new ball of strong convection with cold cloud tops it shouldn't either. The system seems to be in decent shape at present with good cyclonic curveature, despite some moderate shear and drier air to its west.

Steering currents are presently weak and so Aletta is presently drifting. System should start to find itslef in slightly less shear again as the sub-tropical jet stream pushes northwards into Mexico. Also worth noting that sea surface temps below this system are pretty decent so there is no reason at all that the system shouldn't get stronger. For now I'dll say that the NHC prediction of 55kts is probably quite close to the mark making it a fairly strong Tropical storm however the chances are there, esp if it can drift further east away from the drier air, that the system can close in on hurricane status providing it keeps itslef away from the shear and dry air.

[Mondy]

Hey, kold.

This shows the areas very well. It's really only split in two since i put the original shot up earlier (matter of hours)

[crimsone]

000

WTPZ41 KNHC 290851

TCDEP1

TROPICAL STORM ALETTA DISCUSSION NUMBER 9

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP012006

200 AM PDT MON MAY 29 2006

MICROWAVE SATELLITE IMAGERY AROUND 03Z INDICATED THE CENTER OF

ALETTA HAD REMAINED WELL-DEFINED AS THE CYCLONE CONTINUED TO

DRIFT SLOWLY NORTHWARD. HOWEVER...SINCE THE LAST MICROWAVE

OVERPASS... INFRARED SATELLITE IMAGERY INDICATES DEEP CONVECTION

AND POSSIBLY A SMALL CDO HAVE DEVELOPED OVER THE LOW-LEVEL CENTER.

THE INITIAL INTENSITY OF 40 KT IS BASED ON A BLEND OF SATELLITE

ESTIMATES OF 35 KT FROM TAFB AND SAB...45 KT FROM AFWA...AND THE

RECENT DEVELOPMENT OF THE CDO-LIKE CONVECTIVE FEATURE.

THE INITIAL MOTION ESTIMATE REMAINS 360/02 KT...BASED ON MICROWAVE

POSITION ESTIMATES BETWEEN 00Z AND 03Z. ALL OF THE NHC MODEL

GUIDANCE SUGGESTS THAT A GRADUAL TURN TOWARD THE NORTHWEST OR

WEST-NORTHWEST SHOULD OCCUR WITHIN THE NEXT 24 HOURS AS MID-LEVEL

RIDGING TO THE NORTH AND NORTHWEST OF ALETTA SLOWLY DEVELOPS

EASTWARD. THE MODELS ARE IN EXCELLENT AGREEMENT ON THIS EVOLVING

SCENARIO...AND THE ONLY DIFFERENCE BETWEEN THE MODELS LIES IN HOW

FAST THEY MOVE ALETTA WESTWARD AFTER 72 HOURS. THE UKMET APPEARS TO

BE TOO FAST IN THE LATTER PERIODS...WHICH HAS CONTAMINATED THE GUNA

AND GUNS CONSENSUS FORECASTS. AS A RESULT...THE OFFICIAL FORECAST IS

SLOWER THAN GUNA AND IS SIMILAR TO THE PREVIOUS FORECAST TRACK.

THE MUCH ADVERTISED DECREASE IN THE VERTICAL SHEAR OVER THE PAST

COUPLE OF DAYS FINALLY APPEARS TO BE OCCURRING. UPPER-LEVEL OUTFLOW

HAS IMPROVED TO THE WEST...AND THE DEVELOPMENT OF THE CDO-LIKE

FEATURE COULD BE THE ONSET OF MORE SIGNIFICANT INTENSIFICATION...

MAINLY IN THE SHORT TERM. THE SHIPS MODEL DECREASES THE VERTICAL

SHEAR TO ABOUT 5 KT BY 24 HOURS...AND THEN GRADUALLY INCREASES THE

WEST TO SOUTHWESTERLY SHEAR TO 20-25 BY 48 HOURS AND BEYOND.

THEREFORE... THE INTENSIFICATION TREND WAS INCREASED A LITTLE BIT

ABOVE THE SHIPS MODEL FORECASTS THROUGH 48 HOURS...AND THEN IS CLOSE

TO THE SHIPS INTENSITY FORECASTS AFTER THAT.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 29/0900Z 16.2N 101.0W 40 KT

12HR VT 29/1800Z 16.4N 101.2W 45 KT

24HR VT 30/0600Z 16.4N 102.0W 50 KT

36HR VT 30/1800Z 16.4N 102.7W 55 KT

48HR VT 31/0600Z 16.4N 103.4W 55 KT

72HR VT 01/0600Z 16.3N 104.7W 50 KT

96HR VT 02/0600Z 16.0N 106.0W 50 KT

120HR VT 03/0600Z 16.0N 107.5W 45 KT

$$

[*Stormforce~beka*]

Whats a CDO??

[crimsone]

It stands for Central Dense Overcast. Its an area at the center of the low containing intense storm activity. In a hurricane, it's the area encompasing the eyewall and the eye.

Being that this isn't a hurricane though (yet, at least), it's simply the center of the storm, with high cloudtops and intense thunderstorm activity, which is shows that the low center has intense convection and is strengthening (It's the cyclones "heat engine" showing itself clearly - a sign of better organisation)

[Mondy]

[crimsone]

There's no banding on that Tropical Storm... apparently

[Mondy]

Whilst Aletta begins to die, what's the script with the mass in w.GOM??

Looks more potent than Aletta

Edited May 29, 2006 by Mondy the clumsy

[crimsone]

Slightly off-topic, but just for you monds ...

MID-UPPER RIDGING IS WEST OF THE UPPER TROUGH IN THE CENTRAL/WEST GULF WITH THE UPPER AXIS ALONG 89W/90W. THESE FEATURES ARE ENHANCING UPPER LEVEL DIFFLUENCE IN THE W GULF WHICH IS PRODUCING CONSIDERABLE CLOUDINESS AND A FEW CLUSTERS OF MODERATE CONVECTION N OF 20N BETWEEN 93W-97W.

I'm not conviced that Aletta is about to die though.

http://www.ssd.noaa.gov/goes/flt/t1/loop-vis.html

Edited May 29, 2006 by crimsone

[kold weather]

I'll be breif with this post, but system now appears to be starting to move away from the coast. Still a TS but now only bearly as convection wanes quite badly, though thereis still enough deep convection present to keep the LLC covered and shear has decreased a fair amount since yesterday so I think this will be a breif wind-down from Aletta, I'm not quite sure exactly why mind you as I've not had a good look today!

[Mondy]

Ta, Crimsone...the whole area has become less convective now - looked quite impressive earlier..

[crimsone]

000

WTPZ41 KNHC 300229

TCDEP1

TROPICAL DEPRESSION ALETTA DISCUSSION NUMBER 12

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP012006

800 PM PDT MON MAY 29 2006

ALETTA IS STRUGGLING FOR SURVIVAL. THE CLOUD PATTERN IS HIGHLY

DISORGANIZED AND THERE IS LITTLE...IF ANY...DEEP CONVECTION

ASSOCIATED WITH THE CYCLONE. AN AMSR-E IMAGE FROM SEVERAL HOURS AGO

SUGGESTED THAT THE LOW-LEVEL CIRCULATION WAS POORLY DEFINED. THE

SYSTEM IS BEING DOWNGRADED TO A 30-KT TROPICAL DEPRESSION BASED ON A

DVORAK CURRENT INTENSITY ESTIMATE FROM TAFB...AS WELL AS THE

CURRENTLY DISHEVELED APPEARANCE OF THE TROPICAL CYCLONE. ALETTA IS

EXPECTED TO REMAIN IN A RATHER DRY MID-LEVEL AIR MASS...AND WESTERLY

VERTICAL SHEAR IS FORECAST TO BEGIN INCREASING IN ABOUT 12 HOURS.

THESE FACTORS...ALONG WITH THE CURRENT TREND...WOULD APPEAR TO

MITIGATE AGAINST RE-STRENGTHENING. NO CHANGE IN STRENGTH IS

FORECAST FOR THE NEXT COUPLE OF DAYS...AND ALETTA IS FORECAST TO

WEAKEN TO A REMNANT LOW BY 72 HOURS. NEEDLESS TO SAY...THE LATTER

EVENT COULD OCCUR SOONER.

INITIAL MOTION IS SLOWLY WESTWARD...270/3. GLOBAL MODELS FORECAST A

WEAK LOW- TO MID-LEVEL RIDGE TO THE NORTH OF ALETTA FOR THE NEXT

SEVERAL DAYS. THIS REGIME SHOULD MAINTAIN A GENERALLY WESTWARD

MOTION THROUGH THE FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS

SIMILAR TO THAT FROM THE PREVIOUS PACKAGE.

FORECASTER PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL 30/0300Z 16.0N 102.3W 30 KT

12HR VT 30/1200Z 15.9N 102.8W 30 KT

24HR VT 31/0000Z 15.8N 103.7W 30 KT

36HR VT 31/1200Z 15.7N 104.5W 30 KT

48HR VT 01/0000Z 15.6N 105.6W 30 KT

72HR VT 02/0000Z 15.5N 107.5W 20 KT...REMNANT LOW

96HR VT 03/0000Z 15.5N 109.5W 20 KT...REMNANT LOW

120HR VT 04/0000Z 15.5N 111.5W 20 KT...REMNANT LOW

Bye Bye Aletta. It was fun while it lasted, and good practice for the rest of the season with your twists and turns and re-directs, and difficulty in forecasting.

[P.K.]

WTPZ41 KNHC 300857

TCDEP1

TROPICAL DEPRESSION ALETTA DISCUSSION NUMBER 13

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP012006

200 AM PDT TUE MAY 30 2006

DEEP CONVECTION HAD BEEN ABSENT FROM ALETTA FOR ABOUT EIGHT HOURS

UNTIL IT RESUMED AROUND 04Z THIS MORNING. WHILE THE RECENT BURST HAS

PERSISTED FOR A FEW HOURS... THE CONVECTION IS NOT ALL THAT WELL

ORGANIZED. THE INITIAL INTENSITY IS MAINTAINED AT 30 KT BASED ON A

BLEND OF THE 06Z DVORAK ESTIMATES. CIRRUS CLOUDS ARE PASSING FROM

NORTHWEST TO SOUTHEAST OVER THE LOW-LEVEL CENTER... INDICATIVE OF

THE INCREASING SHEAR THAT HAS CONTRIBUTED TO THE WEAKENING OF THIS

SMALL CYCLONE SINCE YESTERDAY... AND THE ENVIRONMENT APPEARS FAIRLY

STABLE AND DRY. GIVEN HOW MUCH ALETTA HAS STRUGGLED AGAINST THESE

CONDITIONS DURING THE PAST 24 HOURS... AND SINCE WESTERLY SHEAR IS

FORECAST BY THE GLOBAL MODELS TO ROUGHLY DOUBLE IN MAGNITUDE DURING

THE NEXT 24-36 HOURS... RESTRENGTHENING DOES NOT APPEAR LIKELY. THE

NEW OFFICIAL FORECAST ANTICIPATES THE CYCLONE TO DEGENERATE INTO A

REMNANT LOW WITHIN ABOUT 36 HOURS... A BIT FASTER THAN INDICATED IN

THE PREVIOUS ADVISORY.

THE DEPRESSION CONTINUES MOVING SLOWLY WESTWARD AT ABOUT 4 KT TO THE

SOUTH OF A WEAK LOW- TO MID-LEVEL RIDGE. THE EVENTUAL REMNANT LOW

IS EXPECTED TO MAINTAIN A GENERAL WESTWARD OR WEST-SOUTHWESTWARD

MOTION FOR SEVERAL DAYS... ALTHOUGH THE LOW COULD LOSE ITS IDENTITY

SOONER THAN SHOWN IN THE FORECAST.

FORECASTER KNABB

FORECAST POSITIONS AND MAX WINDS

INITIAL 30/0900Z 16.0N 102.8W 30 KT

12HR VT 30/1800Z 15.9N 103.3W 30 KT

24HR VT 31/0600Z 15.8N 104.2W 25 KT

36HR VT 31/1800Z 15.6N 105.1W 20 KT...REMNANT LOW

48HR VT 01/0600Z 15.3N 106.0W 20 KT...REMNANT LOW

72HR VT 02/0600Z 15.0N 107.5W 20 KT...REMNANT LOW

96HR VT 03/0600Z 15.0N 109.5W 20 KT...REMNANT LOW

120HR VT 04/0600Z 15.0N 111.5W 20 KT...REMNANT LOW