Satellite images and Curaçao radar on Friday afternoon showed TD 9 bringing heavy rainfall to the ABC Islands and the northern coast of South America, but struggling with strong wind shear: The low-level center was exposed and the system was relatively few severe thunderstorms were confined to the southwest side of the center. The reason: Outflow from powerful Hurricane Fiona brought strong northeasterly winds over TD 9, creating about 20-25 knots of wind shear. Otherwise, conditions were favorable for growth, with warm sea surface temperatures of 29–30 degrees Celsius (84–86°F) and a humid atmosphere (average relative humidity of 70%). At 11 a.m. EDT Friday, TD 9 was 515 miles east-southeast of Jamaica, with peak winds of 35 mph, heading west-northwest at 14 mph. Figure 1. Topography of Cuba. The island has a number of mountain ranges that are likely to disrupt TD 9 if the storm crosses one of them. (Image credit: Wikipedia)

Intensity forecast for TD 9

Continued high wind shear from Fiona’s upper-level outflow is expected to hinder TD 9’s development through Saturday morning, and its close proximity to the South American coast may also hinder it. Chances of development will increase by Saturday afternoon as Fiona approaches Canada, allowing wind shear over TD 9 to drop into the moderate range, 10-20 knots. Very favorable development conditions are expected Saturday night when TD 9 will be in the central Caribbean: There, it will find very warm water of 30-31 degrees Celsius (86-88 °F) with high heat content, light air shear, extremely outflow channels high and humid atmosphere (mid-level relative humidity 70%). The entire northern half of the Caribbean is free of tropical cyclones all season, so these pristine waters (running about 0.5 degrees Celsius or 0.9 degrees Fahrenheit above average for late September) will be particularly ripe for the support of any well organized cyclone with favorable atmospheric conditions. The two intensity forecasts from the National Hurricane Center so far have been unusually aggressive. Friday’s initial forecast at 5 a.m. EDT predicted that TD 9 would reach 110 mph winds by the end of the five-day forecast period. This forecast is only the third time the NHC has made such an aggressive forecast in the first advisory for a new system. The other two cases also involved western Caribbean systems: Hurricane Ida in 2021 and Hurricane Iota in 2020. Both of these hurricanes ended up rapidly intensifying into Category 4 storms, exceeding the NHC’s initial intensity forecast. Figure 2. Intensity forecasts for TD 9 available as of 8 AM. EDT Friday, September 23, 2022. The leading intensity model making 4- and 5-day forecasts for Hurricane Fiona, the HWRF model (called HWFI in this plot), was predicting TD 9 to reach Category 9 strength 4 in six days, as was the peak intensity model from 2021, HMON (called HMNI in this chart). (Image credit: tropicaltidbits.com) The NHC forecast for Friday at 11 a.m. EDT for TD 9 was also very aggressive, expressly predicting rapid intensification. Beginning Sunday morning, when TD 9 will be south of Jamaica, the NHC predicted that TD 9 will transition from a tropical storm with winds of 50 mph to a Category 1 hurricane with winds of 85 mph in 24 hours. This meets the minimum definition of rapid intensification, which is an increase in winds of 35 mph in 24 hours. Continued intensification is forecast on Monday as TD 9 passes through the Cayman Islands and approaches western Cuba. The passage of Cuba is likely to interrupt the intensification process, and if TD 9 passes over one of the more mountainous parts of the island (Figure 1), it is possible that the storm will take a day or more to recover and continue to intensify . In addition, TD 9 may be hampered at that time by an increase in wind shear, as an upper-level low west of Cuba brings a southerly flow of upper-level winds over the storm. The NHC currently has TD 9 surpassing a Category 3 hurricane with winds of 115 mph Wednesday morning off the coast of southwest Florida, but that forecast should be considered highly uncertain. TD 9 could conceivably be as weak as a Category 1 hurricane or as strong as a Category 4 hurricane as it makes its closest approach to Florida next week (see Tweet below). See more Using NHC mean intensity errors over the past five years and Friday’s 11 a.m. advisory. EDT for #TD9 , this is what a cone of intensity uncertainty might look like. pic.twitter.com/GPeHrOoHhW — Brian McNoldy (@BMcNoldy) September 23, 2022 It would not be a surprise if TD 9 rapidly intensified at a greater rate than the NHC predicts: the western Caribbean is a notorious breeding ground for major hurricanes and the top intensity model for making 4- and 5-day forecasts for Hurricane Fiona. the HWRF model predicted that TD 9 would reach Category 4 strength in six days, as did the peak intensity model from 2021, HMON (Figure 2). See more Strong tropical storm-force winds could reach south Florida by Tuesday morning, at which point the hurricane watch could be lifted by Sunday morning. Similar chances for hurricane force winds in Tampa and Miami, so don’t let anyone tell you that one part of the peninsula needs to prepare more than another at this point. pic.twitter.com/DoHq3erJEp —Dr. Rick Knabb (@DrRickKnabb) September 23, 2022

Prediction track for TD 9

The spread in track model solutions for TD 9 continues to be large, with impacts in Central America, the Yucatan Peninsula of Mexico, Jamaica, the Cayman Islands, Cuba, Florida, and the Bahamas. As of early Friday afternoon, Central America appears to be at relatively low risk of immediate damage, although heavy rainfall from the storm may affect coastal Honduras beginning Sunday. Mexico’s Yucatan Peninsula is not in the NHC cone, but some of the 12Z Friday GFS ensemble forecast members showed TD 9 passing very close to the northeastern tip of the peninsula, so residents there should pay attention to future forecasts. TD 9’s final track will depend largely on what happens over the next 24 hours, when the storm will be weak and subject to significant position changes. These can occur due to relatively subtle changes in the rudder flow and from reshaping of the center as wind shear tears through the core of TD 9. By Saturday, when TD 9 will have stronger circulation and become a tropical storm, we will have much better idea where it’s going. It looks very likely that Jamaica will miss a direct hit, but the island will still receive 4-8 inches of damaging rain. The Cayman Islands could take a direct hit and Cuba is very likely to take a direct hit, possibly from a major hurricane. The threat to Florida is murkier, with most of the peninsula south of the Panhandle in the NHC’s 5-day cone of uncertainty. Residents of the western Bahamas should also pay attention as they are also in the 5-day cone of uncertainty. All of these areas should be given a high priority in preparations for the storm’s arrival.

Hurricane Fiona will hit Atlantic Canada

One of the strongest storms in Canadian history is expected late Friday into Saturday as Category 4 Hurricane Fiona quickly turns into a massive and powerful post-tropical cyclone just hours before landfall. Rare hurricane and tropical storm warnings have been issued by Environment Canada for an area of ​​about 800 miles, from eastern New Brunswick and southeastern Quebec to Nova Scotia and most of Newfoundland and Labrador. See more “This is going to be a significant and historic weather event for Nova Scotia,” says John Lohr, the provincial minister responsible for the Office of Emergency Management, part of the multi-agency update now underway. pic.twitter.com/C5KARZqVn5 — Brett Ruskin (@Brett_CBC) September 22, 2022 From 11 am EDT Friday, Hurricane Fiona was moving northeast at 35 mph with top sustained winds of 130 mph, about 250 miles north of Bermuda, according to the National Hurricane Center (NHC). Despite this long distance, Fiona’s extended circulation brought sustained winds of 64 mph to LF Wade International Airport in Hamilton just after 8 a.m. ADT, with gusts to 93 mph around 7 a.m. The heavy rain had left Bermuda by late Friday morning. Fiona was producing large swells that created dangerous rip currents along much of the US coast and Canadian shipping. Fiona’s wind field will expand even further before the storm reaches Canada. As Fiona speeds north over unusually warm mid-latitude waters, it is expected to remain a strong hurricane until Friday night, perhaps maintaining Category 3 strength. An approaching upper-level cold front and storm will trigger a which has recently been classified as instant warm insulation. Like Hurricane Sandy’s “superstorm” transition just before it hit New Jersey in October 2012, the approaching mid-latitude storm will wrap Fiona around and quickly become a massive subtropical storm system, but with a warm core of the hurricane still hidden (isolated). As with Sandy, Fiona’s effects will be essentially those of a hurricane, even if the official classification changes in the hours before landfall, which is why Environment Canada has gone ahead with hurricane warnings. As Fiona develops on Friday night, her central pressure may drop to surprising levels. Many models are predicting Fiona to reach Nova Scotia on Saturday…