Tropical Depression 31, which formed in the central Caribbean on Friday morning, is expected to intensify into powerful Hurricane Iota by Sunday. Iota is predicted to bring catastrophic rains of 20-30 inches next week to portions of Central America still recovering from last week’s devasting Hurricane Eta, which hit northern Nicaragua as a category 4 storm with 140 mph winds on November 3.

At 10 a.m. EST Friday, TD 31 was 310 miles south-southeast of Kingston, Jamaica, headed west-southwest at 7 mph. The system had top winds of 35 mph, with a central pressure of 1007 mb. Satellite imagery showed that TD 31’s heavy thunderstorms were confined to the southeast side of the center of circulation, but were steadily becoming more organized. Upper-level winds out of the west were creating a light 5-10 knots of wind shear, keeping TD 31 from forming heavy thunderstorms on the storm’s northwest side.

TD 31 brought flash flooding and heavy rains of three to five inches to Puerto Rico and the Virgin Islands on Wednesday; TD 31 brought up to four inches of rain along the southwestern coast of the Dominican Republic on Thursday.

The first Hurricane Hunter mission into TD 31 is scheduled for Saturday.

Track forecast for TD 31

TD 31 is predicted to move west-southwestward through Saturday morning at about 5-10 mph, under the steering influence of a ridge of high pressure to its north. By Saturday afternoon, this ridge will slide to the east, resulting in a more westerly to west-northwesterly motion of TD 31 through Wednesday. On this track, TD 31 will pass about 300 miles south of Jamaica on Saturday, then make landfall near the Nicaragua/Honduras border on Monday, as predicted by the European and UKMET models.

However, in a worst-case scenario for Honduras, Guatemala, and Belize, TD 31 could slide just north of Honduras, moving parallel to and just offshore of the coast, allowing the storm to maintain its strength longer and subjecting the region to much higher rainfall totals. This is the prediction of the HWRF and HMON models and many of the members of the GFS ensemble forecast. At present, there is almost no model support for the idea that TD 31 might move northward into the Gulf of Mexico and threaten the U.S., as so many other storms this year have done.

Intensity forecast for TD 31

The intensity forecast from the National Hurricane Center’s first advisory for TD 31 at 10 a.m. EST Friday was an unusually aggressive one, calling for the storm to intensify from 35 mph to 110 mph – to the brink of category 3 status – in just 72 hours. According to an analysis of NHC forecasts by Sam Lillo, this is the fastest rapid intensification ever predicted by NHC for a tropical depression. Senior NHC hurricane specialist Eric Blake commented in a Friday morning Tweet, “You don’t see NHC forecast 75 mph of strengthening in 72 hours from a tropical depression very often (rapid intensification for that time period, and on a first forecast, too). Speaks to the really conducive environment ahead!”

As one might surmise from the NHC forecast, conditions for development will be favorable for development of TD 31 through Tuesday, with the SHIPS model predicting light wind shear less than 10 knots, warm sea surface temperatures of 29 degrees Celsius (84°F), and a moist atmosphere with a mid-level relative humidity of 65-70%. The 12Z Friday SHIPS model gave a 51% chance that TD 31 would follow the NHC intensity forecast, and increase its winds by 75 mph in 72 hours. This probability is 10 times higher than the climatological mean.

These conditions are very similar to what Hurricane Eta experienced in its formative stages in the Caribbean in late October, and TD 31 is a significant threat to intensify into a major hurricane that will affect the same areas of the Caribbean impacted by Hurricane Eta. In particular, Nicaragua and Honduras, which were devastated by Hurricane Eta, appear at great risk of receiving heavy rains from TD 31 beginning on Sunday, with NHC calling for 20-30 inches of rain next week.

Eta and Iota: an unprecedented double catastrophe for Honduras

Hurricane Eta brought catastrophic rains to Honduras last week, triggering flooding that devastated the northwestern portion of the country. According to Jeff Ernst, writing in The Guardian, in the valley surrounding San Pedro Sula in northwestern Honduras, rains of over 20 inches fell, and several rivers and flood canals overflowed so high that tens of thousands were trapped for days on rooftops without food or water. Some families waited more than three days for rescue. San Pedro Sula is the country’s second-largest city and economic engine, and the San Pedro Sula Valley is home to over 2 million people.

The official death toll in Honduras stood at 63 on November 10, but the total number of victims is probably in the hundreds, and will likely never be known. Economic damage has been estimated to between $3 billion and $5 billion, 12-21% of Honduras’ GDP.

In Nicaragua, where Eta initially made landfall, damage is estimated at over $178 million (1-2% of GDP), and two deaths are being blamed on the storm. Nicaragua, in contrast to Honduras, did not have heavily populated areas receive rains in excess of 10 inches.

Eta’s final flood: seven killed in North Carolina before Eta becomes post-tropical

After a lifespan of over 10 days, four landfalls, hundreds of deaths, and billions in damage, Tropical Storm Eta finally became post-tropical on Friday morning over the waters off the North Carolina coast. According to Dr. Phil Klotzbach of Colorado State University, Eta’s 10.25 days as a named storm (not including the time it was a tropical depression) made it the Atlantic’s longest-lived named storm forming in November since the Jamaica Hurricane of 1912, which lasted 10.5 days.

Eta helped trigger heavy rains of up to 8.52 inches that fell in a swatch from South Carolina, through North Carolina, and into southeastern Virginia on Wednesday and Thursday (Figure 4). The resulting floods claimed at least seven lives. The rains were caused by a moist flow of Atlantic air in advance of Eta, which interacted with a frontal boundary – a phenomenon called a predecessor rain event (PRE). Eta also contributed directly to the rains. In addition, Eta is being blamed for one death in Florida, an electrocution in Bradenton. The amount of precipitable water (the total water vapor and liquid water in the atmosphere) on Wednesday morning at Wallops Island, Virginia, was the most ever recorded in November (2.11 inches).

Theta poses little threat to land

There was little change on Friday to Tropical Storm Theta, the record-breaking 29th named storm of the 2020 Atlantic hurricane season. At 10 a.m. EST Friday, Theta was located about 470 miles south-southeast of the Azores Islands, headed east at about 12 mph. Theta had top sustained winds of 60 mph.

Theta will move east through Sunday, taking the storm toward the Canary Islands. High wind shear and cold waters are expected to weaken Theta to a post-tropical cyclone with 35 mph winds by Sunday.

Typhoon Vamco rapidly strengthens en route to Vietnam

Long-suffering Vietnam – which has already been affected by 10 named storms this year – is now bracing for number 11.

Typhoon Vamco surged from category 1 to category 3 strength in just six hours on Friday, with top winds pegged at 115 mph by the Joint Typhoon Warning Center as of 7 a.m. EST Friday. Located about 330 miles east of Da Nang, Vietnam, Vamco is passing through a zone of unexpectedly favorable upper-air support, with outflow channels on either side favoring the storm’s rapid strengthening.

Also see: October 2020 was fourth-warmest October on record, NOAA and NASA report

As Vamco moves toward Vietnam, the upper-level support will weaken and the typhoon will be moving over waters cooler than 26 degrees Celsius (79°F), but it may still reach the coast of northern Vietnam as a minimal category 1-equivalent typhoon on Sunday or Monday local time.

Bob Henson contributed to this post.

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Posted on November 13, 2020(3:22pm EST).