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By: wxchaser97 , 11:27 AM GMT on October 15, 2013
Tropical Depression Octave
Octave is a sheared, decoupled tropical cyclone. Octave developed from a disturbance of the SW Mexican coast that slowly acquired a pronounced surface circulation with organized convection. TD-15E formed at 0300Z on Sunday the 12th. As the depression continued to organize, it was quickly upgraded to tropical storm strength. While Octave was forecast to only remain a weak tropical storm, it was able to strengthen into a strong tropical storm several hundred miles off the Mexican coast. As southwesterly wind shear increased, Octave began to weaken. This same shear is what has caused the decoupling of the low and mid level centers. Microwave and satellite imagery show pretty clearly that this decoupling event has happened. The weakening low-level center is located on the southern Baja Peninsula while the convection is located over the Gulf of California and the Mexican mainland. ASCAT and OSCAT passes from a few hours ago, along with current surface obs, still show that the low-level circulation still is pretty well-defined, but is weakening. The latest NHC advisory information and satellite image can be found below.
2:00 AM PDT Tue Oct 15
Location: 25.5°N 112.0°W
Moving: NNE at 5 mph
Min pressure: 1004 mb
Max sustained: 35 mph
Forecast for Octave
Not much can be said about Octave's future besides "no bueno". Octave is interacting with land which is disrupting the low-level circulation. The strong southwesterly wind shear is not decreasing and will continue to adversely impact the depression. To add to this, dry air is also entrained into the system and should further suppress the redevelopment of convection. Looking at current satellite trends and the continuation of an unfavorable environment, Octave should become a remnant low later today. The circulation should continue to lift northeast in response to a strong trough to the northeast. Steering currents are weak, however, and whatever is left of Octave should move slowly into Mexico's mainland over the next 1-2 days. Models are in agreement of the track and intensity of Octave. Moisture from Octave should continue to enhance precipitation over Texas in the next couple days. This is good for the drought situation but some flash flooding has occurred in spots. There will also be locally heavy rain over Northern Mexico.
INIT 15/0900Z 30 KT 35 MPH
12H 15/1800Z 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 16/0600Z 20 KT 25 MPH...POST-TROP/REMNT LOW
All tropical storm warnings have been discontinued.
Tropical Storm Priscilla
TS Priscilla is a weak tropical storm over the open waters of the East Pacific. Deep convection has been mostly confined to the western side of Priscilla due to vertical wind shear from Octave. There has been a developing burst of deep convection over the center over the past couple hours. It will be interesting to see how long this are of convection is able to persist under the unfavorable conditions. Satellite intensity estimates still support Priscilla being a tropical storm. While the satellite appearance is rather poor, I have seen multiple worse looking tropical storms than Priscilla. The latest NHC advisory info and satellite image can be found below.
2:00 AM PDT Tue Oct 15
Location: 17.1°N 116.0°W
Moving: N at 8 mph
Min pressure: 1004 mb
Max sustained: 40 mph
Forecast for Priscilla
There are some mixed signals for whether Priscilla will be able to strengthen in the short term before conditions become unfavorable overall. Easterly wind shear is decreasing over the storm and is expected to decrease further over the next day. This is good for Priscilla as it can then try and develop deep convection fully over the low-level center without it being sheared away while further tightening up said circulation. The decrease in easterly shear is due to the weakening of Octave and its outflow. In theory, this should give Priscilla a 36hr window to organize before shear increases to unfavorable levels. However, there are other forces that will be working against Priscilla. Large amounts of dry, stable air are surrounding the system, especially to the west. SHIPS analysis shows the mid-levels only getting drier as time goes on. This dry air could easily interact with Priscilla and slow the organization of Priscilla. Also, SST's will be decreasing to marginal levels in about 24hrs. With a more marginal thermodynamic environment, there will be less energy available to help sustain the tropical cyclone. After about 48hrs, the atmosphere becomes increasingly unfavorable and any organization would be halted and reversed. Models aren't showing much in the way of strengthening over the short term either. The majority of the models slowly weaken Priscilla from here on out. Giving her the benefit of the doubt, I will forecast her to retain TS strength for the next 12hrs followed by weakening. Priscilla should become a post-tropical cyclone in about 4 days.
Priscilla is moving to the north at 8mph. This is in response to a weakness to its NNE. This weakness is due to Octave, though it is more shallow now, and a strong trough over the US. As Octave dissipates and the trough moves farther to the east, mid to upper level ridging should build over the Eastern Pacific. This would turn Octave to the NW. As the ridge amplifies more in 3-4 days, Priscilla should turn more to the west. The majority of dynamical, statistical, and global models take Priscilla off to the west. There are a few models that diverge late in the forecast period, but they won't verify. Priscilla should remain far from land and bring no significant impacts to any landmasses.
INIT 15/0900Z 35 KT 40 MPH
12H 15/1800Z 35 KT 40 MPH
24H 16/0600Z 30 KT 35 MPH
36H 16/1800Z 30 KT 35 MPH
48H 17/0600Z 25 KT 30 MPH
72H 18/0600Z 20 KT 25 MPH...POST-TROP/REMNT LOW
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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