Tropical Depression Four

The area of low pressure we have tracked across the western Caribbean Sea and Bay of Campeche has become a tropical depression, the fourth of the 2016 Atlantic season. As of the latest NHC advisory, the following information was available on the cyclone:

Wind: 35 mph, with gusts to 45 mph
Location: 20.1°N 95.4°W
Movement: W/275 degrees at 7 mph
Pressure: 1009 mb

After a lull in convection earlier in the day, the depression has made a comeback this evening. A small burst of very cold convection has enveloped itself directly over the low-level center, with some evidence of more tightly-wound convective banding developing just west of the center. Although current satellite estimates only support 30 kt, I suspect the aircraft will find a tropical storm in the next few hours.

Figure 1. Latest infrared satellite image of Tropical Depression Four. Image credit: NOAA’s Satellite Services Division (SSD).

The depression appears to have decelerated a bit over the last several hours, likely due to tucking itself underneath the newly-developed convection. The motion should soon stabilize and the cyclone should gradually assume a more speedy westward to west-northwestward trajectory. Synoptically, the depression is locked into a non-capricious pattern, with a strong mid-level ridge located over the western Gulf Coast. The southeasterlies to the south of this ridge should push the depression slowly west-northwest toward the coast of eastern Mexico, with the guidance generally agreeing on a landfall not long after 12z Monday. My forecast closely mirrors that, but is just a little slower than the guidance to account for the current motion and more organized structure, particularly after the system is inland.

The tropical cyclone is over 29C SSTs, and the surrounding environment is considerably less dry and sheared than yesterday; the cyclonic westerlies over the northwestern Gulf of Mexico have been replaced with anticyclonic easterlies, signifying a departure of the upper-level trough that was plaguing that portion of the Gulf yesterday. The only obvious inhibiting factor to strengthening is time, but the aforementioned conditions should enable the depression to become a tropical storm before landfall. If that occurs, it will be the earliest occurrence of the fourth named storm in the historical record, surpassing Tropical Storm Debby in 2012 (June 23) and Hurricane Dennis in 2005 (July 5). After moving inland, the depression will do its typical rapid decay over the mountains of eastern Mexico.

The primary hazard with the cyclone will remain heavy rain, flash floods and mudslides, especially in areas of mountainous terrain; this will be the case even should the system become a tropical storm.

A tropical storm warning is in effect for portions of eastern Mexico.

Intensity forecast

Initial 06/20 0300Z/11 PM EDT Sun 20.1°N 95.4°W 30 kt 35 mph
12 hour 06/20 1200Z/8 AM EDT Mon 20.2°N 96.4°W 40 kt 45 mph
24 hour 06/21 0000Z/8 PM EDT Mon 20.3°N 97.1°W 40 kt 45 mph: inland
36 hour 06/21 1200Z/8 AM EDT Tue 20.4°N 98.4°W 25 kt 30 mph: inland post-tropical/remnant low
48 hour 06/22 0000Z: dissipated

Track forecast

Figure 2. My forecast track for Tropical Depression Four.

NHC storm information

000
WTNT34 KNHC 200231
TCPAT4

BULLETIN
TROPICAL DEPRESSION FOUR ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042016
1000 PM CDT SUN JUN 19 2016

…TROPICAL DEPRESSION EXPECTED TO BRING HEAVY RAINFALL TO
PORTIONS OF EASTERN MEXICO…

SUMMARY OF 1000 PM CDT…0300 UTC…INFORMATION
———————————————–
LOCATION…20.1N 95.4W
ABOUT 145 MI…230 KM ESE OF TUXPAN MEXICO
ABOUT 80 MI…130 KM NE OF VERACRUZ MEXICO
MAXIMUM SUSTAINED WINDS…35 MPH…55 KM/H
PRESENT MOVEMENT…W OR 275 DEGREES AT 7 MPH…11 KM/H
MINIMUM CENTRAL PRESSURE…1009 MB…29.80 INCHES

WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY:

None

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for…
* Laguna Verde to Rio Panuco Mexico

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area.

For storm information specific to your area, please monitor
products issued by your national meteorological service.

DISCUSSION AND 48-HOUR OUTLOOK
——————————
At 1000 PM CDT (0300 UTC), the center of Tropical Depression Four
was located near latitude 20.1 North, longitude 95.4 West. The
depression is moving toward the west near 7 mph (11 km/h), and
this general motion is expected to continue over the next day
or two. On the forecast track, the center of the depression is
expected to move inland over eastern Mexico on Monday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Some slight strengthening is forecast, and the depression could
become a tropical storm before it makes landfall in Mexico on
Monday.

The estimated minimum central pressure is 1009 mb (29.80 inches).

HAZARDS AFFECTING LAND
———————-
RAINFALL: The depression is expected to produce total rainfall
accumulations of 6 to 10 inches with isolated maximum amounts of 15
inches possible in higher terrain over the Mexican states of
Veracruz, Tamaulipas, San Luis Potosi, Queretaro, Hidalgo, and
northern Puebla. These rains could cause life-threatening flash
floods and mud slides.

WIND: Tropical storm conditions are expected to first reach the
coast within portions of the warning area Monday morning, making
outside preparations difficult or dangerous.

NEXT ADVISORY
————-
Next intermediate advisory at 100 AM CDT.
Next complete advisory at 400 AM CDT.

$$
Forecaster Brown0.1