Tropical Depression 14 formed in the southwestern Gulf of Mexico’s Bay of Campeche at 11 a.m. EDT Saturday, and appears poised to develop into Hurricane Milton, which will hit Florida’s west coast on Wednesday. This situation – which involves an unusual storm track, together with the potential for rapid strengthening – has evolved quickly and should be taken quite seriously by Floridians, especially along the West Coast.
TD 14 in the formative stages
At 11 a.m. EDT Saturday, TD 14 was located 210 miles (340 km) north-northeast of Veracruz, Mexico, moving north-northeast at 3 mph (6 km/h), with top sustained winds of 35 mph (55 kph) and a central pressure of 1007 mb. Satellite loops and Brownsville, Texas radar showed that TD 14 had a modest-sized area of heavy thunderstorms with plenty of rotation, which were steadily growing more organized and bringing heavy rains to the coast near the Texas/Mexico border.
Track forecast for TD 14
TD 14 will be in an area of weak steering currents through Sunday, then move at an increasing forward speed east-north to northeast under the steering influence of a trough of low pressure to its northwest. On this path, TD 14 is expected to make landfall on the west coast of Florida Wednesday while moving at a forward speed of about 15 mph (25 km/h). This is a very unusual path for a tropical cyclone: Few systems form in the western Gulf of Mexico and then move eastward and make landfall as a hurricane on the Florida Gulf Coast. One such historical analogue in October was an Oct. 28, 1859 category 1 hurricane that hit Tampa (see Tweet below). Given that we are now in early rather than late October, and given that climate change has boosted sea surface temperatures since the mid-1800s, TD 14 will likely pass over substantially warmer waters than did the 1859 hurricane.
The models are fairly unified in bringing TD 14 shore over Florida’s west coast along some of the most heavily populated areas, between Fort Myers and Tampa Bay. Importantly, TD 14 will be approaching at close to a perpendicular angle, from the west-southwest, rather than the more common approach to Florida’s west coast from a southernly angle. Perpendicular approaches tend to have lesser track errors, because a slight change in trajectory is not amplified by the track being largely parallel to the coast. However, the distribution of large urban areas scattered along Florida’s West Coast means that even small track differences could have important local effects.
There is somewhat more uncertainty with TD 14’s timing versus its track. The time of landfall among the five high-resolution hurricane models that made a 6Z Saturday forecast had a about a 14-hour range, between 1 p.m. EDT Wednesday and 3 a.m. EDT Thursday. NHC predicted landfall will occur earlier than this, near 9 a.m. EDT Wednesday, but mentions: “Users are reminded to not focus on the exact forecast track or timing at the longer range as the average NHC 4-day track error is about 150 miles (240 km).” (This can be produced by errors in timing as well as trajectory.)
Intensity forecast for TD 14
Conditions will be very favorable for intensification of TD 14 through Tuesday. Ocean temperatures in the western Gulf of Mexico are record-warm – 30-31 degrees Celsius (86-88°F), about 1-2 degrees Celsius above average. Moreover, a substantial amount of warm water extends to great depth (i.e., the ocean has a high ocean heat content). Wind shear is predicted to be light, less than 10 knots, and the atmosphere will be very moist, with a mid-level relative humidity of 70-80%. These conditions should allow TD 14 to become Tropical Storm Milton by Sunday, and Hurricane Milton by Monday.
On Tuesday and Wednesday, when TD 14 will be in the central and eastern Gulf of Mexico, the intensity forecast grows more complex. There will be plenty of dry air to the north that the storm will begin wrapping towards its core, though it currently appears that wind shear will remain low, and this dry air will have trouble penetrating into the storm’s core. Ocean temperatures along TD 14’s track will drop by about a degree Celsius, but they will remain more than ample to support a hurricane, and the storm will be passing over a region with warm water that extends to great depth—the Loop Current. TD 14 will be passing over the same stretch of of ocean that Hurricane Helene traversed at the end of September, but Helene’s passage did not cool the waters of the eastern Gulf very much, since it was moving at a high forward speed. As TD 14 approaches Florida, it will be near a region of strong upper-level winds to its northeast, associated with the jet stream, which will provide a very favorable upper-level outflow channel (as well as increased wind shear).
The 11 a.m. EDT Saturday official forecast from NHC called for TD 14 to peak Wednesday morning just below major hurricane strength, as a Cat 2 with 110 mph (175 kph) winds. However, this forecast may be conservative, as NHC noted, and a number of intensity models predict that TD 14 will become a Cat 3 or Cat 4 hurricane (Fig. 2). The DTOPS model gave a 67% chance that TD 14 would intensify by at least 75 mph (120 kph) in the 72 hours ending at 8 a.m. EDT Tuesday, making it a high-end Cat 2 with 110 mph (175 kph) winds.
A dangerous and destructive storm surge likely for Florida
If TD 14 follows the current NHC forecast and hits a heavily populated portion of Florida as a high-end Cat 2, storm surge damage will be in the billions, and could exceed $10 billion. TD 14 is predicted to be an average-sized hurricane near the time of landfall, with tropical storm-force winds that extend out up to 150 miles (240 km) from the center. But since the storm will be pushing its storm surge over the large area of shallow waters off the west coast of Florida, a large and destructive storm surge can be expected. Assuming that TD 14 hits at high tide and is at category 2 strength, water levels in excess of 6 feet (1.8 m) above normally dry ground are likely for about a 100-mile swath of the coast near and to the right of where the center makes landfall. A storm surge in excess of 9 feet (2.7 m) would likely occur along a 20-mile stretch of coast where the right-front eyewall traverses. NHC’s storm surge risk map for a category 2 hurricane (Fig. 3) shows the areas at highest risk.
A serious flood and wind threat for Florida
Forecast models show that a moist flow of air over Florida in advance of the arrival of TD 14 will trigger a Predecessor Rain Event (PRE) on Sunday and Monday for both sides of the Florida peninsula – from Tampa southward on the west coast, and from Vero Beach southward to Miami on the east coast. The arrival of TD 14 on Wednesday will generate additional heavy rainfall, with 5-day total amounts of 6-10 inches (150-250 mm) being common across much of Florida.
Wind damage will also be a major concern from TD 14, and may extend considerably far inland, since the system is expected to be moving at a brisk forward speed of about 15 mph.
The first hurricane hunter mission into TD 14 is scheduled for early Sunday morning.
Bob Henson contributed to this post. We may not have a new post until Sunday evening or midday Monday, but will put updates in the current post until then.
