Tropical weather analysis - June 10, 2012
A broad area of low pressure continues to spin in the vastness of the eastern Pacific, centered about 850 miles south of the southern tip of Baja California.
Figure 1. Latest infrared satellite image of Invest 93E. Image credit: NOAA's Satellite Services Division (SSD).
This system actually looks less organized than 24 hours ago due to easterly shear, which is why I wasn't in the mood to call for rapid intensification in the previous forecast. The SHIPS analyzes 19 kt of easterly shear over the system as of 0z. Normally in this basin, such shear would not cause a signification disruption of the cloud pattern -- at least to the point where strengthening is downright inhibited -- since most systems here tend to move relatively fast, offsetting the net shearing effect of the Pacific ridge. However, 93E is moving at only about 10 mph, slower than the shear vector. Using a combination of satellite and microwave fixes, the low-level center appears to be located east of the convection. The banding isn't particularly impressive, either.
SHIPS still wants to make this system a hurricane in about four days, yet keeps a distinct shearing mechanism in place. This seems mysterious to me, but it is not the first time I've seen SHIPS incorrect. The current cloud pattern notwithstanding, water vapor imagery suggests that the large scale environment is not yet unfavorable enough to deter slow strengthening. It is most interesting that none of the models, in sharp contrast to yesterday, want to develop this system into anything more than a weak tropical storm. One thing I've learned over the years is to not jump the gun based on a new day -- or cycle -- of model runs, and I will make no such exception here. Since there is little apparent reason, other than easterly shear, why this system should not strengthen, I am still calling for slow development over the next couple of days, and this low could still become a tropical depression or tropical storm.
The system is expected to continue to track slowly west to west-northwest over the next several days. A southwestward motion is still possible in the long-term, but I am not ready to commit to this.
Probability of genesis within the next 48 hours: 50%
More Eastern Pacific development possible
The global models continue to insist that another tropical cyclone will develop behind 93E in a few days. There is no obvious reason why this should not happen, and at the very least I am confident in an organized area of disturbed weather developing. The synoptic pattern favors an eventual turn toward the Mexican coast, but the details are too broad and variable to be adequately worked out at this time.
Atlantic development still possible in the long-range
Based on the forecast of the large scale pattern over the United States and western Atlantic, there is still the potential for some type of tropical development in the western Caribbean beginning late this week into early next week. Although the models are less enthusiastic about this today, I am not ready to back off on this just yet, given the widespread influence of the upward MJO forecast to make its way into our segment of the world at those ranges. In addition, global models still have immense difficulty in properly resolving large scale perturbations within the synoptic scale pattern, so that daily fluctuations in prognostications are not uncommon. I still believe a Caribbean system, at least a tropical disturbance, is possible in six to seven days, but there is enough uncertainty that it may not become a tropical cyclone. These models also hint at possible mischief off the eastern seaboard, presumably from a portion of the energy from the Caribbean disturbance interacting with a decaying frontal trough.