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By: wxchaser97 , 2:00 AM GMT on November 03, 2013
Tropical Depression 18-E
Tropical Depression 18-E still remains disorganized as it slowly gets closer to the Baja Peninsula. The low-level and mid-level circulations remain tilted and the center is mostly removed from the deep convection. Moderate easterly shear continues to cause problems for the depression. It isn't allowing the low and mid-level centers to align which would thus put deep convection over the center. However, The center looks to be becoming better defined and is slowly moving closer to the convection, a sign that shear is slowly lessening. Satellite estimates and reliable scatterometer data are starting to indicate that 18-E might be close to TS strength. While SAB remains at T1.5/20kts, TAFB is up to T2.5/35kts, and scatterometer data has shown wind vector with increased magnitude than earlier. The current NHC advisory info and satellite image can be found below.
5:00 PM PDT Sat Nov 2
Location: 17.9°N 109.9°W
Moving: NW at 6 mph
Min pressure: 1006 mb
Max sustained: 35 mph
Forecast for TD 18-E
Tropical Depression 18-E has still failed to reach tropical storm strength. The aforementioned easterly shear has halted the organization of 18-E's structure. There have been signs that this shear may be decreasing a little over the system. This can be seen on UW-CIMSS shear maps and satellite images. The uncertain part with this forecast is how much more the vertical shear will lessen over 18-E and for how long. If shear can decrease enough, then 18-E should have enough time to intensify into a tropical storm. However, if the shear doesn't decrease enough, for a long enough period of time, then 18-E won't have enough time to organize before it encounters a harsher environment. The latest GFS shows a little more favorable upper air pattern for about the next 24hrs, which would be enough time for organization. The SHIPS analysis also shows shear decreasing some until the 24-36hr mark. Going off of that, 18-E definitely still has a shot to become a TS before a southwesterly shear component sharply increases as a trough moves near. However, I do have my doubts that 18-E will be able to recover. Another thing to consider is the area of dry air to the west of 18-E. Luckily for the system, the current shear vector is from the east and thus not advecting that dry air into the system. Dry air entrainment may become an issue when the southwesterly shear becomes stronger, but that would only be lesser issue. Finally, 18-E is situated over warm waters and will remain over warm SST's until landfall. That is about the only truly good thing going for the depression at this point. Intensity models reflect this marginal environment in their intensity forecasts. Most models show 18-E staying at 30kts or only strengthening to 35kts. The GFS and ECMWF don't show much strengthening at all of 18-E either. For the sake of continuity and the slight lessening of shear, I am still forecasting 18-E to become a tropical storm. However, I don't think it will be able to become anything more than a 35kt TS. TD 18-E should weaken quickly when it makes landfall due to friction and the loss of its heat source, most likely dissipating by 72hrs.
The center of TD 18-E has been difficult to locate on conventional satellite images since it formed. While the center was more defined on visible satellite images today, the sun has set over TD 18-E so there are no visible images. Luckily, timely microwave passes caught the center of 18-E. The initial motion still appears to be to the NW at about 6mph. Going off of microwave images, I'd put the center at around 18.1N 110.0W. UW-CIMSS steering maps also show the NW movement of 18-E. TD 18-E has been moving around the southwest periphery of a subtropical ridge located over Mexico. The depression should continue to move around the periphery of the ridge for about the next day, turning to the NE as it does this. By then the ridge will be sliding east as a mid-level trough moves in from the NW. This feature should continue to steer 18-E to the NE, but it will also quicken the forward motion of the depression. TD 18-E should make landfall in Mexico in 36 to 48 hours from now. Global and dynamical models are in fair agreement in the track of 18-E. There are some subtle differences in the exact timing of the turn to the NE on the model runs. The ECMWF and most of the dynamical models bring 18-E into the coast near Culiacan, MX, with the GFS being a little farther to the NW. Given the agreement in the model guidance, my forecast track is very similar to them and the NHC. TD 18-E may bring locally heavy rain and gusty winds to the SW Mexican coast. Due to the small threat of tropical storm-force winds, a tropical storm watch has been issued for a small portion of the SW Mexican coast by the Mexican government. The remnant mid-level moisture from 18-E may help enhance rainfall in the southern US in conjunction with a mid-latitude cyclone over the Great Plains.
INIT 03/0000Z 30 KT 35 MPH
12H 03/1200Z 35 KT 40 MPH
24H 04/0000Z 35 KT 40 MPH
36H 04/1200Z 35 KT 40 MPH
48H 05/0000Z 25 KT 30 MPH...POST-TROP/REMNT LOW
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* TOPOLOBAMPO TO LA CRUZ
A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.
INTERESTS IN BAJA CALIFORNIA SUR AND ELSEWHERE IN WEST-CENTRAL
MAINLAND MEXICO SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.
The Atlantic basin is quiet
The Atlantic hurricane season is officially over in about 28 days. However, the season is acting like it already wants to be done. There isn't any legitimate threats of development in the basin right now. An area of disturbed weather is locate in the central Caribbean. It has no reliable model support and isn't in a very favorable environment to develop. Conditions aren't expected to get much more favorable and the NHC hasn't highlighted this area for the potential to develop. Basin wide, conditions are getting more unfavorable as we get farther into fall. Climatologically, wind shear has been increasing in the Atlantic, SST's/TCHP have been decreasing, and the air has been becoming more stable. Fronts have been dropping into the GOM and west Caribbean, which has decreased SST's and increased shear. Reliable models aren't hinting at the development of anything in the near future. Of course, there could be a spin-up in the BOC or W Carib off of the tail end of a front or something, but that is unlikely in my opinion. If the Atlantic doesn't get any development in the next 1-2 weeks, then it is safe to say the Atlantic season is done as a MJO pulse moves out of our area. I'll hopefully be able do a full write-up on the Atlantic in the end of November when I'm on Thanksgiving break.
Have a great night and don't forget to set your clocks back an hour tonight as daylight saving time ends.
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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