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 , 6:10 AM GMT on August 15, 2013
Tropical Depression Five
Tropical Depression Five formed over the eastern Atlantic near the Cape Verde Islands late Wednesday. As of the latest NHC intermediate advisory, the following information was available on the cyclone:
Wind: 35 mph, with higher gusts
Location: 14.2°N 24.2°W
Movement: WNW at 14 mph
Pressure: 1008 mb
The intensity of the tropical cyclone is a little difficult to estimate this evening. On one hand, 0z Dvorak numbers from TAFB and SAB were only at 1.0, the very bottom of the scale, but an ASCAT pass near 0z showed winds near tropical storm force to the east of the center. In addition, the satellite presentation is impressive, with the center presumed to be located along the eastern portion of the deep convection.
Figure 1. Latest infrared satellite image of Tropical Depression Five. Image credit: NOAA's Satellite Services Division (SSD).
I presume the depression is near tropical storm strength, but even if it's not quite there yet, environmental conditions appear favorable for a steady intensification until around 48 hours, when the SHIPS model and objective SST analyses suggest that the depression will encounter cooler water, and consequently, a slightly more stable airmass. None of the guidance suggests significant strengthening over the next few days, and the GFS shows westerly shear increasing in about 72 hours due to a developing cold low over the central Atlantic. The depression is expected to move into warmer waters late in the period, which may offset the potential for westerly shear, and allow for at least a steady state storm. I have memories of Dorian, which also struggled in this same area, however, so it will be most interesting to monitor future intensity trends. It is possible that the cyclone strengthens a little more than forecast in the short-term. It should also be noted that conditions may become more favorable beyond day five, with a considerable decrease in vertical shear.
The depression is moving steadily west-northwest, to the south of a weak mid-level ridge. An upper low over the northeastern Atlantic is maintaining a sizable weakness to the north of the tropical cyclone. However, this feature is forecast to gradually retreat northward over the next few days, and the cyclone is expected to respond by turning westward at longer ranges. The guidance remains in a decent agreement on the synoptic pattern for a system still in its formative stage, and my forecast track is similar to, but a little south of, the latest NHC prediction.
It is too early to speculate whether or not the depression will recurve out to sea as most Cape Verde cyclones do, or if it will continue westward and potentially threaten land at extended ranges. My best guess right now, based on the pattern, is that the system still stands a chance at recurving, but that the odds are currently against it doing so. We will have to monitor future trends carefully.
Because of the close proximity to the Cape Verde Islands, a tropical storm warning has been issued for a portion of that archipelago.
Intensity forecast and positions
INITIAL 08/15 0300Z 14.0°N 23.5°W 30 KT 35 MPH
12 hour 08/15 1200Z 14.3°N 25.0°W 35 KT 40 MPH
24 hour 08/16 0000Z 14.5°N 27.5°W 40 KT 45 MPH
36 hour 08/16 1200Z 15.1°N 31.8°W 45 KT 50 MPH
48 hour 08/17 0000Z 15.7°N 35.0°W 50 KT 60 MPH
72 hour 08/18 0000Z 16.4°N 38.5°W 45 KT 50 MPH
96 hour 08/19 0000Z 16.8°N 42.0°W 45 KT 50 MPH
120 hour 08/20 0000Z 16.9°N 46.1°W 45 KT 50 MPH
Figure 2. My forecast track for Tropical Depression Five.
NHC storm information
WTNT35 KNHC 150541
TROPICAL DEPRESSION FIVE INTERMEDIATE ADVISORY NUMBER 1A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013
200 AM AST THU AUG 15 2013
...CENTER OF THE DEPRESSION PASSING SOUTH OF THE CAPE VERDE
SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
ABOUT 55 MI...90 KM SSE OF FOGO IN THE CAPE VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES
WATCHES AND WARNINGS
CHANGES WITH THIS ADVISORY...
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE SOUTHERN CAPE VERDE ISLANDS OF MAIO...SANTIAGO...FOGO...AND
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN THE
NEXT 12 TO 24 HOURS.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE OF THE
UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
DISCUSSION AND 48-HOUR OUTLOOK
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL DEPRESSION FIVE
WAS LOCATED NEAR LATITUDE 14.2 NORTH...LONGITUDE 24.2 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 14 MPH...22
KM/H...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE DURING THE
NEXT COUPLE OF DAYS. ON THE FORECAST TRACK...THE CENTER OF THE
CYCLONE SHOULD MOVE TO THE SOUTH AND SOUTHWEST OF THE SOUTHERN CAPE
VERDE ISLANDS TODAY.
MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...
AND THE DEPRESSION IS EXPECTED TO BECOME A TROPICAL STORM LATER
THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB...29.77 INCHES.
HAZARDS AFFECTING LAND
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED OVER THE SOUTHERN CAPE
VERDE ISLANDS TODAY. STRONGER WINDS ARE LIKELY IN AREAS OF HIGHER
TERRAIN ON THE ISLANDS.
RAINFALL...TROPICAL DEPRESSION FIVE IS EXPECTED TO PRODUCE TOTAL
RAIN ACCUMULATIONS OF 2 TO 4 INCHES OVER THE SOUTHERN PORTION OF
THE CAPE VERDE ISLANDS.
NEXT COMPLETE ADVISORY...500 AM AST.
An area of low pressure, associated with a tropical wave, is located over the western Caribbean Sea about 150 miles east of Chetumal, Mexico. I am not impressed by the organization with this system, with a recent ASCAT pass and a couple of buoy observations suggesting that the wave axis is not well-defined. In addition, convection has essentially evaporated over the last several hours, which suggests that 92L is not self-sustaining, losing its convection during diurnal minimum.
Figure 3. Latest infrared satellite image of Invest 92L. Image credit: NOAA's Satellite Services Division (SSD).
Despite the recent downward trend in convection, atmospheric conditions still appear favorable for the formation of a tropical depression over the western Caribbean or southern Gulf of Mexico, although if this occurs, it is likely to be in the Gulf, since 92L is progressing steadily west-northwestward toward Yucatan. I should note that the intensity forecast for this system is rather tricky; there is little shear over the southern Gulf, but the shear vector there is northerly, which is not a favorable combination for a northward-moving system. On the other hand, upper-level winds are favorable where the low is currently at, but again, due to time constraints, 92L is unlikely to become a tropical cyclone prior to crossing Yucatan within the next 12-18 hours. Also, the GFS still shows westerly shear increasing markedly north of 25N over the Gulf, so while the system may try to develop some in the southern Gulf, my current thinking is that this may no longer happen, primarily because the circulation is still not closed.
Regardless of development, heavy rainfall and gusty winds will accompany this system over portions of the Yucatan Peninsula and Belize; this weather will eventually spread up to the northern Gulf Coast.
My favored landfall point right now is southeastern Louisiana near Grand Isle in about 72 hours, although water vapor imagery shows the Texas ridge building eastward into central Louisiana, so it is possible this could be too far west if this trend persists.
It's also worth noting that, regardless of whether the system becomes a tropical cyclone, the primary band of weather will be found to the east of the center due to shear, making the landfall point of little consequence.
Probability of development in 48 hours: 50%
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