Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 2:14 AM GMT on June 10, 2014
Tropical Depression Three-E
The tropical disturbance that has paralleled the coast of southern Mexico over the last few days has become a tropical depression. As of the 5 PM EDT NHC advisory, the following information was posted on the depression:
Wind: 35 mph, with higher gusts
Location: 15.4°N 102.0°W
Movement: W at 5 mph
Pressure: 1006 mb
Most of the convection is confined a persistent band to the east of the center, but recent satellite data suggests that it could be forming and becoming more persistent over the center while the outer band slowly contracts. There is currently no hard data suggesting the depression has become a tropical storm, and I expect the National Hurricane Center will keep the winds at 30 kt at the upcoming advisory. Upper-tropospheric outflow is well-defined, implying an environment of light vertical shear.
Figure 1. Latest infrared satellite image of Tropical Depression Three-E. Image credit: NOAA's Satellite Services Division (SSD).
Interestingly, a 1640 UTC ASCAT pass captured the circulation of the tropical depression and showed a few isolated wind vectors of 30 kt within the vigorous convective band to the east of the center; using the low-bias of the ASCAT instrument, that would equate to roughly 35 kt at the surface, or the bottom of tropical storm intensity. However, the pass also showed that the circulation was elongated and in its formative stages at the time it revealed those winds, and it is likely that those estimates were rain-contaminated. Nevertheless, if current trends persist and the convection appearing over the low-level center can maintain itself, we should have a short-fuse tropical storm overnight.
Environmental conditions appear quite conducive for intensification... if the cyclone can manage to mix out the pronounced dry slot wrapping into the southern semicircle, a situation which still appears evident based on recent satellite and microwave data. If the dry air can mix out, the depression could certainly intensify much faster than what I have indicated below. Indeed, the SHIPS rapid intensification is currently indicating a 63% chance of a 25-kt increase in wind speed during the next 24 hours, which is 4.8 times the sample mean. While the SHIPS can sometimes be too aggressive in projecting rapid intensification, I have found that it is usually adequate for delineating rapid intensification potential based on in situ atmospheric and oceanic conditions. Also, the Maximum Potential Intensity (MPI) in the path of the depression is approximately 880 mb/150 kt, or quite comfortably in the Category 5 threshold (shown below). While this scenario has a nearly 0% chance of occurring even if the depression rapidly intensifies, it certainly highlights the distinct possibility that the depression could get much stronger than forecast if a well-defined inner core becomes established. For now, my forecast will remain conservative but will trend upward toward the upper end of the current intensity guidance. It is possible that tomorrow's forecast will be forced to show a much stronger hurricane.
Beyond three days, cooler waters, dry mid-level air, and increasing southwesterly shear will likely induce an abrupt weakening trend.
Figure 2. Eastern Pacific Maximum Potential Intensity (MPI) as of June 9. Put simply, the MPI is a theorized upper intensity limit based on the presumption of idealized atmospheric and oceanic conditions comprised of nil vertical shear, abundant moisture, sea surface temperature/oceanic heat content, and upper divergence. The bottom image indicates theoretical wind speed (kt), while the top image shows a theoretical pressure point (mb).
The depression appears to be moving westward to the south of a well-established subtropical ridge over northern Mexico that is being enhanced by an upper-level trough moving through the Arklatex region extending toward the northern Gulf Coast. The global models suggest this general motion should continue with a fairly constant forward speed being maintained. In about 36-48 hours, the tropical cyclone is expected to begin moving west-northwest as it encounters a pronounced break in the subtropical ridge induced by a slow-moving upper-level trough off the coast of central California. While the general guidance agrees on this scenario, there are some subtleties on precisely where and how sharp the depression is going to turn. The GFDL shoots the system northward toward a landfall in southwestern Mexico, while the GFS shows a continued west-northwest motion past Socorro Island. The ECMWF is similar but somewhat farther south, particularly near the end of the period. The CMC maintains the westward motion longer and consequently has a track a smidgeon farther south than the other guidance. My forecast leans toward a blend of the GFS/ECMWF and is a little south of the current NHC advisory during the first 24-36 hours. As the depression approaches a developing col region between an anticyclone to the west and a mid- to upper-level trough to the east over the western United States near the end of the period, its motion is likely to slow, with some of the guidance suggests some erratic and very slow motion by that time.
Initial 06/10 0000Z 15.4°N 102.0°W 30 kt 35 mph
12 hour 06/10 1200Z 15.4°N 103.3°W 40 kt 45 mph
24 hour 06/11 0000Z 15.5°N 104.7°W 50 kt 60 mph
36 hour 06/11 1200Z 16,0°N 106.3°W 60 kt 70 mph
48 hour 06/12 0000Z 16.5°N 108.2°W 75 kt 85 mph
72 hour 06/13 0000Z 17.1°N 110.1°W 75 kt 85 mph
96 hour 06/14 0000Z 18.0°N 112.0°W 60 kt 70 mph
120 hour 06/15 0000Z 19.0°N 114.0°W 45 kt 50 mph
Figure 3. My forecast track for Tropical Depression Three-E.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Comments will take a few seconds to appear.