I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.
By: KoritheMan , 4:26 AM GMT on August 14, 2012
Remnants of TD7
A tropical wave, the remnants of Tropical Depression Seven, continues racing across the central Caribbean Sea. This system has lost much of its thunderstorm activity today. Blending satellite, microwave, and scatterometer fixes, the wave axis appears to be located near 14.3N 78.1W, although I am not certain of this.
Figure 1. Latest infrared satellite image of former Tropical Depression Seven. Image credit: NOAA
Either way, I do not see a particularly favorable environment ahead of the system. It is still well-embedded within the strong trade winds, which is inhibiting low-level convergence and thus convective development. A continuation of this general motion is expected with only a slight decrease in forward speed is expected. The system could enter the far southern Bay of Campeche on Thursday, but the upper air environment on the GFS does not look conducive to regeneration, with a strong westerly flow prevailing south of 25N.
The disturbance may bring heavy rain to portions of Central America and the Yucatan Peninsula over the next several days, but little overall development is anticipated, brief convective bursts notwithstanding.
Probability of development in 48 hours: Near 0%
A tropical wave over the central Atlantic about 1075 miles east-northeast of the Leeward Islands ("93L") is producing limited shower activity. While upper-level winds are favorable for development, water vapor imagery and the convective pattern suggests that the system is still embedded in a subsident airmass.
Figure 2. Latest infrared satellite image of Invest 93L. Image credit: NOAA
The GFS and CMC are predicting that the wave could develop as it find itself beneath a more favorable synoptic environment as it recurves well east of Bermuda on Thursday. Looking at water vapor imagery, I do see more vertical instability available in that area, and 93L could attempt to tap into this moisture, which would promote organization given the favorable upper-level wind pattern shown on the models, which should at the very least be diffluent. I see no reason to discount this at this time; experience has shown that it doesn't take much for weak and sprawling systems like 93L to resurrect themselves once they find a more favorable environment. The system could pose a long-range threat to the Azores, although whether it is tropical or extratropical at that time remains to be seen.
This wave should continue moving west-northwest to northwest at 15 to 20 mph over the next couple of days. A break is noted in the subtropical ridge near 60W between the western and eastern Atlantic ridges, so recurvature should begin close to this longitude.
Probability of development in 48 hours: 10%
Tropical Storm Hector poses no threat to land. As of the most recent NHC advisory, the following was available on the tropical storm:
Wind: 45 mph, with higher gusts
Location: 18.0°N 113.2°W
Movement: W at 6 mph
Pressure: 993 mb
After strengthening a bit today, convection has been well-removed from the center again due to easterly shear. However, a burst has recently developed about 75 miles to the southwest of the estimated low-level center.
Figure 3. Latest infrared satellite image of Tropical Storm Hector. Image credit: NOAA
The easterly shear that has prevented significant development of Hector is expected to continue for the next couple of days. Thereafter, a reduction in the shear is forecast, but the cyclone will be moving over cooler waters by that time. Model guidance is in good agreement with this. In fact, given the shear, a slow decay will likely occur before then. Hector is forecast to become a remnant low in about four days.
The tropical storm remains south of a small but well-established low- to mid-level ridge. The global models suggest this high will gradually weaken over the next couple of days as Hector comes under the influence of a mid-latitude trough that is currently amplifying off the California coast. The global models generally agree with this evolution, but they differ in regards to the depth and amplitude of the upper low and its attendant frontal zone, as well as how Hector will interact with it. The ECMWF and GFDL have a sharper and faster northward turn, while the GFS is farther to the west and much slower. While I am not willing to go quite as slow as the GFS, I tend to prefer its solution overall. My forecast track is in good agreement with that of the National Hurricane Center. Deceleration is forecast near the end of the forecast period as Hector becomes a shallow system steered by the low-level flow.
5-day intensity forecast
INITIAL 08/14 0300Z 40 KT 45 MPH
12 hour 08/14 1800Z 40 KT 45 MPH
24 hour 08/15 0300Z 35 KT 40 MPH
36 hour 08/16 1800Z 35 KT 40 MPH
48 hour 08/17 0300Z 35 KT 40 MPH
72 hour 08/18 0300Z 30 KT 35 MPH
96 hour 08/19 0300Z 30 KT 35 MPH...POST-TROP/REMNANT LOW
120 hour 08/20 0300Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
5-day track forecast
Figure 4. My 5-day forecast track for Hector.
A small area of low pressure over the eastern Pacific is along the southeast coast of Mexico. Although atmospheric conditions are relatively favorable, the close proximity to the coast suggests that any development will be slow. Additionally, since at this point the system is less than 75 miles offshore, it would not take much of a subtle northwestward motion to bring the low ashore and eliminate development potential entirely. In fact, a study of satellite imagery suggests the low could already be inland. On the other hand, earlier ASCAT data still suggested the system was offshore. Lacking any surface observations in the vicinity, it is difficult to tell. I will indicate it to be just offshore, though.
Regardless of development, heavy rainfall will be possible across southern Mexico over the next day or two, which could flooding in areas of orographic terrain.
Probability of development in 48 hours: Near 0%
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