Category 5 Milton poses an exceptionally serious threat to Florida’s west coast » Yale Climate Connections

Intensity forecast for Milton

Between 2 p.m. EDT Sunday and 2 p.m. EDT Monday, Milton’s official top sustained winds increased from 80 to 175 mph, an increase of 95 mph (153 km/h) in 24 hours – not far from Hurricane Wilma’s Atlantic-record 24-hour intensification rate of 110 mph in 2005. Milton intensified from a tropical storm to a Category 5 hurricane in just under 25 hours, just shy of Wilma’s record 24-hour rate. In the 51 hours from 11 a.m. Saturday to 2 p.m. Monday, Milton’s top sustained winds went from 35 to 175 mph – topping Hurricane Felix’s Atlantic-record 54-hour rate of 140 mph (225 km/h) in 2007 by accomplishing the same amount of intensification in an even shorter time frame.

Conditions will be very favorable for intensification of Milton through Tuesday morning. 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, 5-10 knots, and the atmosphere will be moderately moist, with a mid-level relative humidity of 60%.

While Milton may intensify a bit more beyond the astounding strength observed on Monday afternoon, there is a limit to how strong a hurricane can become given its environment – what’s called its maximum potential intensity. For Milton at its current location, that figure is computed to be about 200 mph (320 km/h), with a central pressure around 890 mb.

Ironically, we cannot show Climate Central’s “Climate Shift Index: Ocean” for Milton, showing how much more likely climate change made the record-warm ocean temperatures possible – because the data for that product comes from NOAA NCEI facility in Asheville, North Carolina, which was severely affected by record flooding spawned by Hurricane Helene two weeks ago. Editor’s update, 4:30 p.m. EDT on October 7: Climate Central just issued a new analysis that said, “sea surface temperatures (SST) in the region where Hurricane Milton is developing are at or above record-breaking highs. A rapid attribution analysis determined that those temperatures were made up to 400-800 times more likely by climate change over the past two weeks.”

Ocean temperatures along a long stretch of Helene’s track were made 100-400 times more likely from human-caused climate change.

One factor that is likely to prevent Milton from achieving its maximum potential intensity is an eyewall replacement cycle. Radar loops from the northern Yucatán Peninsula Monday afternoon showed that Milton was a very compact hurricane, with an 11-mile (18 km) diameter eye, and there was a ring of intense thunderstorms forming around this tight eye. This likely signals the beginning of an eyewall replacement cycle, which will cause the inner eyewall to collapse and a new, larger-diameter eye to form from the outer ring of intense thunderstorms. This process, common in intense hurricanes, typically causes the peak winds to drop by 10-20 mph (16-32 km/h) but spreads hurricane-force winds over a larger area, increasing the storm surge potential. Milton’s center will track near the flat landscape of the far northern Yucatán Peninsula on Monday night, putting part of its circulation over land – another factor that could influence Milton’s structure and perhaps reduce its peak winds slightly.

Conditions are expected to get less favorable for Milton Tuesday evening until landfall Wednesday or early Thursday, as Milton moves from the central to the eastern Gulf of Mexico. Strong upper-level winds out of the southwest are predicted to bring a high 25-35 knots of wind shear on Wednesday, and with some very dry air wrapping into the storm from the west, it is expected that the core of the hurricane will get breached, causing significant weakening. Ocean temperatures along Milton’s track will still be very warm, though, and the hurricane will be passing over a region with warm water that extends to great depth — the Loop Current. (Milton will be passing over the same stretch 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 Milton 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. This increased upper-level outflow may allow Milton to resist the assault on its core by the increased wind shear and dry air.

Track forecast for Milton

There is high confidence in Milton’s general track across the Gulf of Mexico. Milton will continue moving toward the east-southeast on Monday, eventually angling east. Models are in agreement on a track that takes Milton’s center near and most likely just north of the coast of the Yucatán Peninsula of Mexico. Hurricane-force winds could extend as far as the immediate coast on Monday night, but the small size of Milton’s central core could also allow such winds to stay just offshore. Residents along the north coast of the Yucatán should continue to monitor Milton closely through Monday night, as only a small rightward shift would bring much more dangerous conditions onshore.

On Tuesday and Wednesday, Milton will gradually loop leftward and accelerate toward the east-northeast and northeast as the hurricane falls under the influence of an upper trough extending through the eastern U.S. from southeast Canada. The major global-scale models are in close agreement on this overall track, which will bring Milton into Florida’s west coast sometime on Wednesday afternoon or evening, most likely near or just south of the Tampa Bay area. Among the most reliable track models, only the UKMET (the green line in Fig. 1 below) has been an outlier, significantly further to the south than the rest, but the 12Z Monday run of the UKMET (not shown in the graphic below) was much closer to the Tampa Bay area than earlier runs. The European model (not shown), which was the best-performing track model in 2023 for lead times up to 72 hours, has been consistent with a landfall in the Tampa Bay area, which is near the center of the National Hurricane Center cone issued at 11 a.m. EDT Monday.

The tougher forecast problems are determining more precisely when Milton will reach the coast (see discussion below) and exactly where it will make landfall. Precision on both of these will gradually improve as landfall draws closer. Here are the average track errors over the past five years of National Hurricane Center forecasts for the Atlantic, as we discussed in a July post:

48 hours = 79 miles (127 km)
36 hours = 60 miles (97 km)
24 hours = 44 miles (71 km)

These errors can be viewed as circles around a given forecast point within the “cone of uncertainty,” so they can occur from leftward or rightward swings as well as speed-ups or slowdowns. Note also that the cone itself is calibrated to encompass about two-thirds of all actual storm locations; in other words, at any given future point, a hurricane can be expected to fall outside the cone about a third of the time.

Given the especially serious potential of Milton, and the high confidence of a Florida west-coast landfall, residents along and inland from the Florida Gulf Coast should base their evacuation decisions on guidance from the National Hurricane Center and local emergency agencies, rather than waiting for more specificity or hoping for some major shift in the forecast.

Milton’s expected track from the western Gulf to the west coast of Florida is unprecedented in living memory. In data going back to 1851, only three hurricanes – all of them prior to 1900 – moved from the vicinity of the Bay of Campeche to make landfall in western Florida. Unlike the more common approach from the south-southwest, Milton’s approach from the west-southwest is giving Milton much more time than usual to evolve over the Gulf before landfall. It also means that winds and storm surge will be aimed more directly at Florida’s west coast, and it raises the odds of strong winds pushing further inland into the peninsula. Wind damage will also be a major concern from Milton, and may extend considerably far inland, since the system is expected to be moving at a brisk forward speed of about 15 mph (24 km/h). A narrow corridor of hurricane-force sustained winds along and just south of Milton’s track could extend as far inland as Orlando.

10/7 10am CDT: There is an increasing risk of life-threatening storm surge from #Milton for portions of the west coast of the Florida Peninsula beginning Tuesday night or early Wednesday.

Residents should follow any advice given by local officials and evacuate if told to do so. pic.twitter.com/NBIqaUdfcB

— NHC Storm Surge (@NHC_Surge) October 7, 2024

A devastating storm surge likely even if Milton weakens to a Cat 2 or Cat 3 at landfall

Milton’s tremendous Cat 5 winds are putting a large amount of ocean water on the move. If Milton weakens significantly to Cat 2 or Cat 3 strength by landfall, as currently predicted by most of the hurricane models, this process will spread Milton’s strongest winds over a wider area of ocean, increasing the volume of water put in motion. When Milton crosses over into the shallow waters of the continental shelf, 90 miles (145 km) offshore of Florida, this swirling water will form a large dome that will push onto the shore, creating a massive and destructive storm surge that will be more characteristic of a Cat 3 or Cat 4 hurricane than a Cat 2 or Cat 3 hurricane. A sobering fact: three of the most destructive Atlantic hurricanes on record were former Cat 4 or Cat 5 storms that were weakening in the 12 hours leading up to landfall. These include the costliest weather disaster in world history (Hurricane Katrina of 2005, with $191 billion in damage; Cat 5 peak, Cat 3 at landfall), Hurricane Rita of 2005 ($28 billion; Cat 5 peak, Cat 3 at landfall), and Hurricane Opal of 1995 ($10 billion; Cat 4 peak, Cat 3 at landfall) (h/t to Matt Lanza).

Milton is currently a small hurricane with tropical-storm-force winds that extend out 80 miles (130 km) from the center. But Milton will be interacting with a low-pressure system to the north of Florida and a front over Florida, which will inject energy into the hurricane, causing its wind field to expand (baroclinic forcing). At the time of landfall, the National Hurricane Center is predicting Milton will be a much larger hurricane, with tropical storm-force winds extending out up to 220 miles (355 km) from the center. This large wind field is likely to bring the highest storm surge on record along an 80-mile (129-km) swath of Florida’s west coast near and to the right of where the eye makes landfall.

The timing of Milton’s landfall will be a significant factor in determining how much coastal flooding occurs. The difference in water level between high and low tide is about 2.2 feet (0.7 m). Low tide at St. Petersburg, Florida, is Wednesday afternoon near 2 p.m. EDT; high tide is at 6 a.m. Thursday. The peak surge (the height of the water above what would normally occur) will occur at the time of landfall, which the National Hurricane Center is currently predicting will be around 8 p.m. EDT Wednesday, or mid-tide. If this timing holds, water levels will be about a foot lower than if Milton were to hit at high tide. However, there is still considerable uncertainty over storm timing.

Current worst-case scenario for Tampa Bay: the 12Z HWRF model

Our five top hurricane-specific forecast models – the HWRF, HMON, HAFS-A, HAFS-B, and COAMPS-TC – have been painting some extremely ugly possible futures for Tampa Bay from Hurricane Milton. Many of the runs have shown a landfall just north of Tampa Bay, which would maximize the surge in the bay. The most devastating scenario for Tampa Bay painted by any of the model runs from 12Z (8 a.m. EDT) Monday was from the HWRF model, which showed Milton hitting as a borderline Cat 3/Cat 4 with 130 mph (210 km/h) winds, hitting just north of Tampa Bay (Fig. 2). Such a storm would likely generate a storm surge in the bay in excess of 10 feet, causing over $10 billion in damage. The 12Z Monday runs of the HMON, HAFS-A, and HAFS-B models were not as strong, showing a landfall at Cat 2 strength near or just north of Tampa Bay.

Rainfall forecast for Milton

Rainfall this week will be widespread across Florida, both ahead of and during Milton. A predecessor rain event far to the east of Milton has brought localized heavy rains across much of the peninsula through the weekend. These rains will continue on Monday, mainly across South Florida, where the National Weather Service Weather Prediction Center has issued a Moderate Risk of excessive rain leading to flash floods, The Moderate Risk extends along and near the coast roughly from Naples south, east, and north to West Palm Beach, including the Everglades.

A temporary downturn in rainfall is expected on Tuesday before a corridor of torrential rain associated with Milton pushes across central and northern Florida from Wednesday into Thursday. A Moderate Risk for excessive rains or flooding is already in effect for that Day 3 period, and a more focused High Risk area may be issued once there is more precision in Milton’s track and structure forecast. Dry air wrapping around the south side of Milton will likely limit rain totals south of the eventual track. Along and north of the track, heavy rains will fall atop soils that in some cases are saturated, exacerbating the risk of tree falls in high winds that could extend well inland.

Bottom line: prepare for the worst. Our post, 30 great tools to determine your flood risk in the U.S., is a good place to go to evaluate your flood risk.