Tropical Storm Melissa: Hurricane Threat to Caribbean | Yale Climate Connections

A Hurricane Warning has been issued for the southern coast of Haiti and a Tropical Storm Warning for Jamaica due to Tropical Storm Melissa, which as of midday Wednesday had not yet strengthened. The storm was moving slowly west-northwest over the near-record temperature waters of the central Caribbean, which have so far been untouched by any hurricane or tropical storm this year.

As of 11 a.m. EDT on Wednesday, Melissa was in the central Caribbean, approximately 325 miles (525 kilometers) southeast of Kingston, Jamaica, with maximum sustained winds of 50 mph (85 km/h) and a central pressure of 1,000 mb, moving west-northwest at just 2 mph (4 km/h). Satellite imagery showed that strong wind shear of 20-25 knots kept the western side of the circulation largely free of intense storms, while the storm’s heaviest rain occurred over waters south of Haiti and the Dominican Republic.

The many possibilities for Melissa’s future over the next five days include several days of torrential rain over some of the most flood-vulnerable areas of the Caribbean. Catastrophic flooding and landslides pose a threat to Haiti, as well as the southern Dominican Republic, eastern Cuba and Jamaica. Due to strong wind shear caused by the location of the subtropical jet from Florida eastward across the Bahamas, Melissa is expected to pose no threat to the continental United States for at least the next week, and ensemble models indicate only a remote possibility that the storm could veer far enough to the northwest to impact Florida.

The Caribbean waters, close to record temperatures, will fuel the growth of Melissa

This week, Melissa will pass through some of the warmest water ever recorded this late in the season across the Atlantic Basin: about 30 degrees Celsius (86°F), about 1.3 degrees Celsius (2.3°F) warmer than average. According to Climate Central’s Climate Shift Index (Fig. 2), human-caused climate change made current heat near Melissa’s location in the central Caribbean 500 to 700 times more likely.

Melissa’s Career Forecast

There is much more uncertainty than usual in Melissa’s trajectory, as it is trapped in an area of weak steering currents, situated between two high-pressure systems. If Melissa manages to rapidly strengthen into a hurricane, its size and vertical extent could allow it to feel the influence of a low pressure trough over the Bahamas, which would drag the storm quickly northward, crossing Haiti or eastern Cuba and reaching the Bahamas by this weekend.

However, the recent trend of the models has been to keep Melissa relatively weak, which would favor a slow movement towards the northwest or west, keeping the system in the Caribbean at least until Monday, October 27. On this track, Melissa would have more time over warm waters and would likely become a major hurricane early next week, as the National Hurricane Center predicts in its 11 a.m. EDT forecast on Wednesday. On this trajectory, the most significant threats that Melissa would present would be to Jamaica, the Cayman Islands, and Cuba.

Intensity forecast for Melissa

Slow strengthening appears to be the most likely option for Melissa over the next three days. The strong wind shear that was affecting Melissa on Wednesday afternoon is expected to decrease to a moderate level of 10-20 knots by Thursday and remain moderate through the weekend. The storm is in an unusually humid atmosphere: Mid-level relative humidity was near 80% on Wednesday and is expected to remain between 70 and 80% through Friday. However, if Melissa makes it to the western Caribbean, she might have to contend with some drier air.

In addition to unusually warm surface waters, the Caribbean currently has extensive ocean heat content that extends to considerable depth (Fig. 4), so even a slow-moving Melissa is unlikely to be greatly hampered by the rise of cooler subsurface waters. The NHC was not forecasting rapid intensification of Melissa over the next three days, but Wednesday’s 12Z SHIPS model forecast indicated a 15% chance of rapid intensification to 35 mph within 24 hours and a 26% chance of rapid intensification to 75 mph within 72 hours. That would put Melissa in a Category 3 on Saturday afternoon, with winds of 125 mph.

The dangers of late-season hurricanes in the Caribbean

Slow moving systems that strengthen in the Caribbean late in the season can cause huge problems. In early October 2016, Hurricane Matthew moved north over far western Haiti as a Category 4 hurricane, dumping more than 20 inches (500 mm) of rain over much of far eastern Cuba and southwestern Haiti, and hitting the Bahamas and several other islands. Matthew caused 731 deaths and more than $16 billion in damage (2016 USD).

Just over 10 years ago, Hurricane Wilma strengthened with astonishing speed into a Category 5 monster in the northwestern Caribbean. Between October 18 and 19, 2005, Wilma set two historical records for the Atlantic basin for rapid intensification, deepening from 975 to 892 millibars (hPa) in 12 hours and from 979 to 882 mb in 24 hours, making it the strongest central pressure hurricane in Atlantic history. Wilma also recorded a record for the largest increase in maximum sustained winds in 24 hours, going from 75 to 175 mph. Wilma made landfall on the Yucatan Peninsula, Mexico, as a strong Category 4 hurricane and moved rapidly northeastward, impacting southwest Florida on October 24 as a Category 3 hurricane. Wilma caused 52 deaths and $26.5 billion in damage (2005 USD).

In late October 1998, then-Category 5 Hurricane Mitch dumped massive amounts of rain on Guatemala, Nicaragua, and Honduras (30 to 40 inches, or 750-1,000 millimeters, in many areas), even as it slowed and weakened, making landfall as a Category 1 hurricane. The flooding and landslides caused approximately $6 billion in damage (1998 USD) and more than 11,000 confirmed deaths, in addition to another 11,000 missing persons without being located. Mitch was the deadliest Atlantic hurricane of the satellite monitoring era (since the 1960s), and possibly since the Great Hurricane of 1780.