Tropical Depression 09E

[Somerset Squall]

The active period continues in the Eastern Pacific, as invest 90E has acquired enough organisation to be classified as a 30kt tropical depression. 09E is currently tracking westwards along the southern periphery of a ridge to the north. The ridge is expected to extend westwards in tandem with 09E, maintaining a general westwards heading. 09E is small, and is prone to rapid intensity changes, both up and down. NHC has admitted that the intensity forecast is highly uncertain. Any significant northward motion would bring 09E over cooler waters, which would cause weakening. If 09E continues directly westwards it could rapidly strengthen as shear remains low and waters would continue to be warm. The intensity could also be affected by something some of the models are showing- the development of another tropical depression east of 09E. A broad disturbance is present several hundred miles east of 09E, which I presume is where this second TD could form. As the disturbance is much larger, some models have been pointing at this system absorbing the tiny 09E. Overall, there are high amounts of uncertainty becuase of the very complex environment- we shall just have to wait and see with this one!

[Cookie]

hopefully we will get another named storm out, as I'd really like to get down to tropical storm rick this year!

[kold weather]

I'm not surprised it was upgraded as it does have a good circulation present with it, however in the last hour or two large outflow boundaries have emerged and as a result the convection has rapidly decreased. Thats because outflow boundaries are a sign the convection is collapsing and we are seeing that occur.

Its possible the NHC were a little hasty in upgrading this one, maybe they should have held at code red for another 6hrs as they were very hasty to upgrade I think. Still this may just be a short term issue and Td9-E should still eventually strengthen again. Conditions aloft aren't bad at all and the SST's are decent so it may just be the Duirnal effects at play here.

[Somerset Squall]

09E has become less organised over the last 24hrs. Moderate to high shear is effecting the small tropical depression, removing most of the convection east of the exposed LLC. As the LLC remains exposed, it hasn't had any opportunity to tighten up. 09E is no longer expected to become a tropical storm, as waters will cool over the next day or so, and, coupled with continued high shear, 09E is likely to dissipate instead.

[Cookie]

it went down hill fast

before

after

523

WTPZ44 KNHC 102038

TCDEP4

TROPICAL DEPRESSION NINE-E DISCUSSION NUMBER 5

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092009

200 PM PDT MON AUG 10 2009

VERTICAL WIND SHEAR...ANALYZED AT 18 KT BY THE SHIPS MODEL...HAS

TAKEN A TOLL ON THE DEPRESSION...LEAVING THE LOW-LEVEL CENTER

EXPOSED FOR A TIME TO THE WEST OF BURSTING DEEP CONVECTION. THE

INITIAL INTENSITY IS HELD AT 30 KT FOR THIS ADVISORY...AND LITTLE

CHANGE IS FORECAST OVER THE NEXT COUPLE OF DAYS...IN GOOD AGREEMENT

WITH MOST OF THE INTENSITY GUIDANCE. ONLY THE SHIPS MODEL SHOWS ANY

APPRECIABLE INTENSIFICATION AS IT PREDICTS THAT THE VERTICAL SHEAR

OVER THE CYCLONE WILL DECREASE TEMPORARILY BETWEEN 36 AND 72 HOURS.

MOST OF THE OTHER GUIDANCE SHOWS FURTHER WEAKENING OR DISSIPATION

AT 72 HOURS AND BEYOND. THE OFFICIAL FORECAST IS FOR THE CYCLONE TO

BECOME A REMNANT LOW BY DAY 4 AND DISSIPATE BY DAY 5...BUT THIS

COULD OCCUR EVEN EARLIER.

THE DEPRESSION APPEARS TO BE MOVING SOUTH OF WEST FOR THE LAST

COUPLE OF HOURS...BUT THE LONGER-TERM MOTION IS ESTIMATED AT

275/10. THE FORECAST TRACK HAS BEEN ADJUSTED TO THE SOUTH OF THE

PREVIOUS PACKAGE AND IS SOUTH OF THE MODEL CONSENSUS. GIVEN THE

INCREASINGLY SHALLOW NATURE OF THE SYSTEM...THERE IS LITTLE REASON

FOR THE SYSTEM TO GAIN MUCH LATITUDE AS IT IS STEERED BY THE

LOW-LEVEL EASTERLY FLOW. MUCH OF THE GUIDANCE SUGGESTS A SOUTHWARD

COMPONENT OF MOTION DEVELOPING LATE IN THE PERIOD...IF THE CYCLONE

SURVIVES THAT LONG. THE FORWARD SPEED IS CLOSE TO THAT OF THE

MULTI-MODEL CONSENSUS TVCN.

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/2100Z 15.1N 124.2W 30 KT

12HR VT 11/0600Z 15.2N 125.6W 30 KT

24HR VT 11/1800Z 15.4N 127.4W 30 KT

36HR VT 12/0600Z 15.6N 129.3W 30 KT

48HR VT 12/1800Z 15.6N 131.3W 25 KT

72HR VT 13/1800Z 15.5N 135.5W 25 KT

96HR VT 14/1800Z 15.5N 139.5W 20 KT...REMNANT LOW

120HR VT 15/1800Z...DISSIPATED

$$

FORECASTER BRENNAN

[Cookie]

just looks really messy imo

[Somerset Squall]

Yes, 09E has really struggled to maintain any convection near the centre for the last 24hrs. Firstly, moderate shear was displacing convection east of the small LLC. Shear has now eased, so there must be some other factor at work here stopping intensification.

CIMSS upper level environment charts show that upper level divergence is poor as was highlighted in the most recent NHC discussion. What this means is the system has a poor exhaust mechanism, the rising air that would fuel convection has nowhere to go and is instead subsiding and choking convection by cutting off the moisture supply. In addition, 09E is moving over waters that were cooled a little recently by Major Hurricane Felicia. The combination of these two factors most likely explain the lack of convection. The lacking convection is leaving the LLC exposed and unable to wind up any further.

09E is located at 15N, 128W:

However, it's not all doom and gloom for 09E. Upper level divergence is expected to improve thus increasing the convection again beyond 24hrs. Shear will remain low, and 09E will be moving over undisturbed warm waters again. These factors favour some intensifcation of the depression. However, the system will need to make a comeback soon or the small TD could not respond to this predicted favourable enviornment. It's worth noting that NHC are once more expecting the depression to eventually become a moderate tropical storm.

[Cookie]

thanks for the great updates

[Somerset Squall]

09E hasn't been able to generate enough convection to remain a tropical cyclone. Dry air and upper level convergence have killed off the system, despite the low shear and warm waters. The LLC is ill defined, and and only isolated, small cells of convection have been coming and going over the last several hours.

The possibility of a moister environment remains further to the west which is where the remnant low is heading. Therefore, regeneration is possible a day or two down the line. However, the remains of 09E may be too weak to respond to these better conditions. We shall see.

[Cookie]

back to a depression again?

[Somerset Squall]

It looks like it may well become a tropical depression again in the near future, yes. NHC give a medium risk (30-50%) chance of this happening within the next 48hrs. Waters remain warm and shear low, so it appears the remnant low has found some moister air based on the recent blow up of convection.

[Somerset Squall]

The remnants of 09E are hard to locate. They have been absorbed into the ITCZ. Therefore, redevelopment is no longer likely.