Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 7:03 AM GMT on July 03, 2013
Dalila strengthened into the third hurricane of the 2013 Pacific hurricane season on Monday afternoon. As of the latest NHC advisory, the following information was available on the hurricane:
Wind: 75 mph, with higher gusts
Location: 18.3°N 107.3°W
Movement: W at 2 mph
Pressure: 987 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
Dalila continues generating rather cold cloud tops, but a couple of recent microwave passes show a deterioration of the inner core structure, the eyewall open to the east. There is a good bit of southeasterly shear over the hurricane, apparently related to a mid-level ridge over the northwestern Caribbean Sea, and also perhaps aided a little by a developing disturbance to the east, although that might be too far away to directly influence Dalila in the short-term.
Figure 1. Latest infrared satellite image of Hurricane Dalila. Image credit: NOAA's Satellite Services Division (SSD).
Dalila has been consistently moving south of the original forecast tracks, which has kept the hurricane over warmer water. While this would normally argue for additional intensification, the global models suggest a continuation of the current shear pattern, and this is favored by glancing at water vapor images as well. The SHIPS suggests the shear will increase further near the end of the period, which would also exacerbate the weakening process. Thus, the forecast calls for steady weakening of the hurricane after 24 hours, with a somewhat more abrupt pace expected at the end of the period.
Water vapor and synoptic data suggest a small kink has developed in the western United States death ridge in association with a small upper trough over western California; this has successfully altered the ridge's orientation such that Dalila appears to now be moving in a west-southwesterly to southwesterly direction, seen using a blend of the various satellite and microwave fixes. There is still some disagreement amongst the models, with the GFS continuing to call for a generally westward-moving cyclone until dissipation, while the ECMWF continues to postulate a more erratic motion; however, it should be pointed out that these models seem to have come into better agreement compared to 24 hours ago, which increases confidence in the forecast. There is still a considerable amount of uncertainty, though, particularly at longer ranges as we wait to see how Dalila interacts with the developing disturbance to the east. It is my feeling that Dalila's vortex will have sufficiently wound down during the end of the forecast period so that the secondary vortex -- then strengthening tropical cyclone -- will begin to nudge the cyclone toward the southeast as Dalila comes under the low-level cyclonic westerly flow associated with the secondary feature.
5-day intensity forecast
INITIAL 07/03 0600Z 65 KT 75 MPH
12 hour 07/03 1800Z 65 KT 75 MPH
24 hour 07/04 0600Z 65 KT 75 MPH
36 hour 07/04 1800Z 60 KT 70 MPH
48 hour 07/05 0600Z 55 KT 65 MPH
72 hour 07/06 0600Z 45 KT 50 MPH
96 hour 07/07 0600Z 35 KT 40 MPH
120 hour 07/08 0600Z 30 KT 35 MPH
For some reason, I'm having trouble posting my track map tonight, so we'll go without one for this forecast package. I apologize.
An area of low pressure located a few hundred miles south of Salina Cruz, Mexico is gradually becoming better organized. While the convection is still broad and unfocused, there has been some subtle hints of convective banding, particularly to the east, and now to the west, where a large and newly-developed band has formed.
Figure 2. Latest infrared satellite image of Invest 97E. Image credit: NOAA's Satellite Services Division (SSD).
There is still some easterly shear over the system, but all of the global models steadily relax this flow over the next 48 hours, which should allow the system to slowly develop. I am anticipating this system to become a tropical cyclone in the next three to four days, and it could occur at the lower end of the estimate if the rate of organization begins to increase. The models suggest this low will move west-northwestward parallel to the coast of Mexico over the next several days, with the possibility of a more northwesterly turn as the system nears the southwest coast of Mexico. It is too early to determine whether or not this system moves inland or not.
Probability of development in 48 hours: 60%
Yucatan Peninsula disturbance
A large area of disturbed weather has developed over the Yucatan Peninsula and western Caribbean Sea, likely in connection with the northern portion of the tropical wave that is poised to produce Tropical Storm Erick in the eastern Pacific. Surface observations and satellite data suggest that the actual surface trough is probably centered over the central Yucatan Peninsula between Campeche and Chetumal, moving slowly west-northwest. Surface pressures are not falling in the western Caribbean Sea, but were relatively low at Merida, Mexico over the last hour, which suggests that the main focus for convergence and thunderstorms is over the Yucatan Peninsula.
The system is in an area of weak steering, with a ridge over the western United States, a cold low/trailing upper trough over the central and southern United States, and another ridge over the western Atlantic and southeastern United States. The global models do not show much change in this pattern for the next two days or so, and it is my expectation that this system will move only slowly over the next couple of days, emerging into the Gulf of Mexico/northern Bay of Campeche in about a day or so. Afterward, the models suggest more progression to the pattern, with the cold low and its attendant trough moving slowly eastward and amplifying southward; this is expected to move the system into the northern or central Gulf Coast by this weekend. The latest I would see the system moving inland is Monday afternoon, and that's likely being generous.
The 0z CMC shows this system moving into southeastern Texas in 96 hours, while the 0z GFS shows it moving into west-central Louisiana in 120 hours. Based on the pattern favoring a slower motion, coupled with the strength of the western United States ridge, I tend to favor the latter solution.
The global models suggest the current westerly shear over the system will gradually relax through the weekend, and the CMC and GFS develop an anticyclone over the system as it approaches the coast, which would promote an environment of light shear. However, the environment never becomes ideal for strengthening, with some southwesterly shear still remaining, and it is possible that the purported anticyclones will become dislodged amidst this flow. Given how little we know about tropical cyclone intensity change, however, I would anticipate anything from a rainy blob to a formidable tropical storm.
Regardless of eventual development, this system is likely to bring a swath of heavy rains and possible coastal flooding to portions of the northern Gulf Coast over the weekend. Interests from Louisiana to the Florida panhandle should monitor the progress of this system. Texas should monitor it as well, but again, given the pattern and the ridge over the western United States, I don't see this making much westward progress, especially since it will be on the back side of the southern United States upper trough as well.
Probability of development in 48 hours: 10%
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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