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Erika’s Path Shifts West; Hawaii Still Watching Ignacio

By: Bob Henson 5:24 AM GMT on August 29, 2015

Thumbing its nose at some of the world’s most skilled computer models and forecasters, Tropical Storm Erika cruised relentlessly almost due west through the northern Caribbean on Friday, failing to make a long-predicted northwestward turn toward the Bahamas. The National Hurricane Center placed Erika's ill-defined center at 11:00 pm EDT Friday at 18.5°N, 72.9°W, or about 40 miles west of Haiti’s capital, Port-au-Prince. Erika’s top sustained winds were set at 45 mph. Hurricane-hunter flights on Friday had found flight-level winds of as high as 55 knots (more than 60 mph) on the north side of Erika.

Erika has been a troubled-looking system, with thunderstorms mostly straggling behind and south of the center due to upper-level northwesterlies producing vertical wind shear (the difference between upper- and lower-level winds) of about 30 mph. Despite the shear, Erika’s large circulation maintained a broad north-to-south oriented region of intense convection through most of Friday before thunderstorms consolidated toward its north end on Friday evening. Most of the core convection passed just south of Puerto Rico, so by and large, the island missed out on the rain that it so desperately needs. San Juan’s Luis Munoz Marin International Airport reported just 0.25” on Thursday and 0.22” on Friday. Heavy rains swept through the Dominican Republic late Friday: a personal weather station in Barahona reported 23.76" of rain between 1 pm Friday and 2 am Saturday, including 8.80" in one hour from 8 pm to 9 pm Friday. Late Friday night, a very intense cluster of thunderstorms was moving slowly across southwestern Haiti, including Port-au-Prince. Deforestation across much of Haiti makes its hillsides especially vulnerable to flash flooding and mudslides, so it appears a difficult night is unfolding for this troubled nation, which has still not fully recovered from the devastating earthquake that killed more than 100,000 people in 2010. According to the Miami Herald, roughly 65,000 Haitians are still housed in tents, with thousands more in precarious housing near flood- and mudslide-prone areas.

Figure 1. Enhanced infrared image of Tropical Storm Erika from the GOES-East floater satellite, collected at 0415 GMT Saturday, August 27 (12:15 am EDT). Image credit: NOAA/NESDIS.

What next for Erika?
It’s tempting to avoid any speculation on what Erika might do, given its behavior in the last 24 hours. Weaker systems often bear to the left, as lower-level winds envelop a larger part of their circulation, so this could be part of why Erika’s path stayed south of nearly all model predictions from just a day earlier. Erika’s motion has resulted in several westward shifts to the NHC-produced cone of probabilities since Thursday. The forecast issued at 11 pm EDT Friday (see Figure 3 below) brings Erika into the extreme eastern Gulf of Mexico as a minimal tropical storm, paralleling Florida’s west coast on Monday and Tuesday. This is roughly consistent with the 0000 GMT Saturday early-cycle update of Friday’s 1800 GMT dynamical models, which takes Erika northward on an inland track through Florida (see Figure 2 below). Not surprisingly, several statistics-based models, which rely heavily on climatology and extrapolation of recent trends, are now taking Erika on a more westward recurvature, through the heart of the Gulf of Mexico. If Erika were to take such an extreme westward track, some rebound in strength would be plausible, since the storm would largely avoid passing over the landmass of Cuba, and deep-layer shear is expected to relax somewhat over the weekend. However, the dynamical models agree that Erika should begin arcing more northwestward across the spine of Cuba on Saturday, with a slower motion to boot. Such a scenario would quickly sound the death knell for Erika as a tropical cyclone, and this is the most probable solution, although a more westward-curving track can’t be entirely ruled out.

Figure 2. Early-cycle track guidance for 0000 GMT Friday, August 28 (left) and Saturday, August 29 (right), show the leftward shift of most dynamical and statistical models. Early-cycle guidance adjusts the model runs carried out in the previous six hours to account for more recent storm behavior. The GFDL model was a noteworthy outlier to the right at 0000 GMT Friday, while several statistical models were leftward outliers at 0000 GMT Saturday. The National Hurricane Center has an online guide to the models abbreviated on these graphics. Image credit: NCAR/RAL Tropical Cyclone Guidance Project.

Regardless of how it’s classified, Erika can be expected to produce large amounts of rain across Cuba this weekend, and the storm or its remnants will likely drench Florida early next week. Some parts of the state could use the rain, but many other parts--especially the western peninsula, including the Tampa area--are already waterlogged after an very wet few weeks (see Figure 4 below). The potential for a weak but large tropical depression to cause widespread flooding should not be underestimated.

Figure 3. The NHC outlook for Erika issued at 11:00 pm EDT on Friday, August 28.

Figure 4. Rainfall across Florida over the 30-day period ending at 8:00 am EDT on Friday, August 28. Image credit: NOAA Advanced Hydrologic Prediction Service.

Figure 5. Hurricanes Ignacio (left) and Jimena (right), in an enhanced infrared image captured by the GOES-West satellite at 0330 GMT Saturday, August 27 (11:30 pm EDT Friday).

Hawaii may dodge a bullet with Ignacio
Hurricane Ignacio continues to plow across the open waters of the Northeast Pacific, still packing winds of 90 mph as of 11:00 pm EDT Friday. Ignacio is located about 720 miles east-southeast of Hilo, Hawaii. Most of the major dynamical models have been consistent in tracking Ignacio about 100 to 200 miles north of the Hawaiian islands, along a west-northwest track roughly paralleling the islands. For a state inexperienced with hurricanes--the Big Island has never recorded one--this is a nerve-rackingly close forecast, but the consistency across models and across time, and Ignacio’s relatively steady track, lends confidence to the forecast. Ignacio is predicted to pass the islands on Monday and Tuesday as a Category 1 hurricane after intensifying to Category 2 strength over the weekend. Sea-surface temperatures are about 2°C (3.6°F) above average, which will help give Ignacio an injection of energy that’s unusual for this part of the Northeast Pacific.

Category 3 Jimena aims for the top
Hurricane Jimena put on a major show of strength Friday, vaulting to a high-end Category 3 rating. Jimena’s top sustained winds were estimated at 125 mph in the NHC advisory issued at 11:00 pm EDT Friday, which makes it the fourth major hurricane of the season in the Northeast Pacific. Jimena’s mostly westward motion is keeping it at low latitudes, with plenty of warm water at the ready, and upper-level conditions are favorable for even more strengthening. NHC is predicting Jimena to continue rapidly intensifying into Saturday, and it may reach Category 5 strength. Last year’s Hurricane Marie was the most recent Category 5 storm in the Northeast Pacific; the strongest on record was 1997’s Hurricane Linda, which packed sustained winds of 185 mph. Jimena’s track will avoid land areas for at least the next five days, and it appears likely to be picked up by a long-range trough before it would approach Hawaii. Longer-range models continue to suggest that Jimena could maintain tropical characteristics up to an unusually high latitude in the Northeast Pacific more than a week from now.

Jeff Masters will be back with our next update on Saturday.

Bob Henson


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