Infrared satellite image at 2 p.m. EDT Monday, August 17, 2020, of two Atlantic tropical waves with potential to develop into tropical cyclones. Superimposed in warm colors are the location of dust and dry air of the Saharan Air Layer, which lay to the north of both systems. (Image credit: University of Wisconsin)

A large and vigorous tropical wave, designated 97L by NOAA’s National Hurricane Center (NHC) at 2 p.m. EDT Sunday, August 16, was bringing heavy rain showers to the southern two-thirds of the Lesser Antilles Island chain on Monday afternoon.

The wave was headed west at about 20 mph – a speed fast enough to impart a shearing action on the disturbance, making development difficult. Otherwise, conditions for development of 97L were favorable, with sea surface temperatures near 29 degrees Celsius (84°F) and moderate wind shear of 10 – 15 knots. The system was embedded in a moderately dry atmosphere with a mid-level relative humidity of 60%. Satellite images showed that 97L had a modest amount of poorly organized heavy thunderstorm activity.

Figure 1. Visible GOES-16 satellite image of 97L at 2:10 p.m. EDT Monday, August 17, 2020. (Image credit: NOAA/RAMMB)

Forecast for 97L

As 97L progresses west to west-northwestward over the next few days, it will slow its forward speed, which should allow increased chances of development. By Friday, when 97L is expected to slow its forward speed to 10 – 15 mph and be in the western Caribbean, very favorable conditions for development may exist. The 12Z Monday run of the SHIPS model predicted that the atmosphere surrounding the system would moisten to a relative humidity of 70%, wind shear would be a light 5 – 10 knots, and SSTs would be a very warm 29.5 degrees Celsius (85°F). The waters of the western Caribbean have the highest heat content of any place in the Atlantic, providing ample fuel for any tropical cyclone that may spin up there.

The 12Z Monday runs of the three best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – did not support intensification of 97L into a tropical depression or tropical storm by Friday. The GFS model predicted development might occur by Saturday, though, when 97L would be entering the Gulf of Mexico. In a 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave 97L two-day and five-day odds of formation of 20% and 50%, respectively. No hurricane hunter missions into 97L are currently scheduled.

Figure 2. Visible GOES-16 satellite image of 98L at 1:30 p.m. EDT Monday, August 17, 2020. (Image credit: NOAA/RAMMB)

Hot on 97L’s heels: a potentially more dangerous threat

A bigger risk of developing into a dangerous threat appears to be a large and complex tropical wave in the eastern Atlantic, located about 500 miles southwest of the Cabo Verde Islands at 2 p.m. EDT Monday. NHC on Monday afternoon designated this weave 98L.

The wave will be moving west to west-northwest at 15 – 20 mph this week. Conditions for development of pre-98L were favorable, with sea surface temperatures near 28 degrees Celsius (82°F) and moderate wind shear of 10 – 15 knots. The system was embedded in a moist atmosphere, with the dry air of the Saharan Air Layer well to the north. Satellite images showed that pre-98L had an impressive amount of heavy thunderstorm activity, but the system had two main centers of action separated by about 500 miles, each developing some spin. The system was struggling over which center to consolidate, which is slowing development.

Forecast for 98L

The future track of 98L will heavily depend upon which of the two areas of action the system ends up consolidating around. In either case, a general west to west-northwest motion can be expected over the next several days. The 12Z Monday runs of the three best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – all supported intensification of 98L into a tropical depression or tropical storm by Friday, when it is expected to be nearing the Leeward Islands. In a 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave 98L two-day and five-day odds of formation of 30% and 70%, respectively.

The next two names on the Atlantic list of storms are Laura and Marco. The earliest twelfth storm in Atlantic tropical history was Luis on August 29, 1995; there is a tie for earliest thirteenth storms, with Lee on September 2, 2011, and Maria on September 2, 2005.

MJO is little help to Atlantic storms early this week – but watch out next week

The Madden-Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the equator that moves around the globe in 30 – 60 days, can greatly increase the odds of tropical cyclone formation when strong and in the proper location. The active portion of the MJO features rising air, which increases thunderstorm updrafts and helps tropical cyclones grow stronger and more organized. Adjacent to the active portion of the MJO is a suppressed portion featuring sinking air, which favors high pressure, drying air, and reduced thunderstorm updrafts.

The U.S. Climate Variability and Predictability Program summarized the MJO’s impact in the Atlantic as follows:

Gulf of Mexico and Caribbean Sea hurricanes are four times more likely to occur when the MJO is producing enhanced precipitation and divergent upper level winds than when precipitation is suppressed and upper level winds are convergent. The modulation of major hurricanes (Categories 3-5) by the MJO is even more pronounced.

This week, the MJO is in a position that favors hurricane activity in the Northeast Pacific, but one that has little signal, either positive or negative, over the Atlantic (though the Gulf of Mexico and western Caribbean will experience some enhancement of conditions favorable for tropical cyclones as the week progresses). The favorable MJO location over the Northeast Pacific is probably partly responsible for the expected rapid intensification of Hurricane Genevieve (see below).

By next week, the most active portion of the MJO is expected to progress eastwards across the Gulf and Caribbean and into the open tropical Atlantic, areas where it is likely to enhance tropical storm activity through the first week of September. The level of enhancement remains uncertain at this point, as computer models disagree on how strong the MJO will be when it reaches the Atlantic.

Also favoring hurricanes next week will be a large-scale region of ascending air over the Atlantic, caused by passage of an atmospheric disturbance called a Convectively Coupled Kelvin Wave, as explained in a tweet by Michael Ventrice.

Figure 3. Visible GOES-17 satellite image of Genevieve at 2:20 p.m. EDT Monday, August 17, 2020. (Image credit: NOAA/RAMMB)

Genevieve seen likely as year’s second major hurricane in the Northeast Pacific

Goosed by the Madden-Julian Oscillation, Hurricane Genevieve was rapidly gaining strength on Monday off the Pacific coast of Mexico, about 750 miles southeast of Cabo San Lucas. Genevieve is passing over slightly warmer than average waters – around 30 degrees Celsius (86°F) – and it is in a near-ideal environment for strengthening, with ample upper-level moisture and light wind shear of only around 5 knots.

Douglas earns a place in hurricane history while sparing Hawaii

The odds of rapid intensification, as calculated by the SHIPS statistical model, are stunning. As of Monday morning, SHIPS gave Genevieve a 95% chance of attaining Category 3 strength (100 knots) by Tuesday morning. That’s more than 15 times greater than the climatological odds! The HWRF and HMON intensity models agree that Genevieve likely will be a major hurricane as soon as Tuesday. According to SHIPS, there is a 65% chance that Genevieve will hit a Cat 4 strength of 140 mph by Wednesday morning. Such rapid intensification is not unheard of, but it’s quite unusual for it to be depicted so strongly in the tools used by forecasters.

Genevieve will track mainly northwest, taking it close to the southern tip of Baja California by Thursday as it encounters cooler waters and drier air. Forecast models are leaning toward a track just offshore, but residents will want to monitor Genevieve closely. The storm could draw close enough to bring high winds and heavy rain to the southern peninsula, and huge surf is a safe bet by midweek.

Bob Henson wrote the Genevieve portion of this post.

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Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

Bob Henson

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance...

69 replies on “Rapidly intensifying Genevieve could become major Pacific hurricane”

  1. Is a Rita track possible where it misses south FL and grazes north Cuba for 98L or is the front too weak and looks like would recurve?

    1. @carmot — the link to your Youtube timelapse vid’s didn’t post in the comments as an URL. So clicking it doesn’t take us anywhere 🙁
      Otherwise, you’d have “billions and billions” of hits 🙂

    2. Sunset thunderstorms firing to the NW of the Northern Mariana Islands? Incredibly beautiful shot!

      1. Thanks. Great guess, but nope. Hopefully I’ll have a timelapse done (in about 2 days?) to prove it. Maybe only about three lighting strikes over 170° of horizon in 150 minutes I was at the beach. All were much later, well after sunset. Cloud anvils closing off as horizon punch hole clouds? Something crazy like that, seriously. That’s all setting sunlight. The sun just set under the right-side LED-red cloud holes. Cheers.

      2. Still capturing sunrises manually without an intervalometer? Man, you are literally a time lapse machine!

        Great videos!

      3. Thanks. I don’t know how familiar you are with photography and ND filters. That’s really not how neutral density filters function. They usually are overall filters, they just cut down on available light for the entire frame – used for long exposures. Like flattening waves or getting lightstreams/star trails. I have three ND filters I can stack, but they won’t help here.

        If you’re talking about graduated ND filters, I don’t have any, they really don’t work well. I also don’t use a square filter system, like Lee or Cokin. I suppose one could cut out an exact size diameter for the sun as a strong ND and place that dot on another filter. In theory, it *might* work. But adjusting and moving it every 3-9 seconds to be in exactly the right position would be tedious at best, nearly impossible IMO. Plus, the size of that dot won’t adapt, if one zooms in or out. Cheers.

  2. Japan Meteorological Agency
    Tropical Cyclone Advisory #9 – 21:00 PM JST August 18 2020
    South China Sea

    At 12:00 PM UTC, Tropical Storm Higos (1000 hPa) located at 21.2N 114.9E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west northwest at 10 knots.

    Gale Force Winds
    120 nm from the center in northeastern quadrant
    90 nm from the center in southwestern quadrant

    Dvorak Intensity: T2.5

    Forecast and Intensity
    24 HRS: 22.9N 110.0E – 35 knots (CAT 1/Tropical Storm) over land southern China
    48 HRS: 23.8N 105.5E – Tropical Depression over land southern China

  3. Atlantic, lock and loaded, To early to tell much but that is going to change in two-three days.

    1. A lot can happen in 7 days but ’tis the season. Crappy timing from the models to put that in the gulf with potential to make a late August landfall. 🙁

    1. It’s working but everone’s at the old digs. Nostalgic and familiar place for so many. YCC, I believe, will be working to add and work on features as the season goes along. YCC Blog will take off eventually; it’s goods to see so much love at the old blog for Jeff, Bob, and their contributors through the years. I take it as a good sign for what this Blog will be soon enough.

      1. I don’t live in Germany. I live in Indiana. Our weather this week is beautiful. Warm days and cool nights. Kind of unusual for August but the local weather guy said we will be seeing many heat waves still to come next week and a few in September.

  4. Japan Meteorological Agency
    Tropical Cyclone Advisory #5 – 9:00 AM JST August 18 2020
    South China Sea

    At 0:00 AM UTC, Tropical Storm Higos (1000 hPa) located at 20.1N 116.7E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west at 16 knots.

    Gale Force Winds
    120 nm from the center in northeastern quadrant
    90 nm from the center in southwestern quadrant

    Dvorak Intensity: T2.0-

    Forecast and Intensity
    24 HRS: 21.1N 112.3E – 45 knots (CAT 1/Tropical Storm) South China Sea
    48 HRS: 22.3N 107.4E – Tropical Depression over land southern China

    1. Are you from the other site? Trying to put together who’s who still… Doing the same. Let’s hope we don’t get any trickery for 15 year anniversary. I would prefer a cloudless, sunny day.

  5. The leading circulation of the two associated with 98L has organized rapidly this afternoon. Circulation and center convection readily apparent.

  6. Cedar Rapids, Iowa may be the canary in the coal mine for 2020 disaster response. Feel horrible for that city. With a supply chain issue this year unlike any we’ve seen in recent years, cumulative effect on this supply chain will likely make later disasters harder to respond to. More logistic bottlenecks happen during the season could leave local officals with very hard calls to make. Officals know this already and the Public needs to know too; so they can prepare with their Neighbors, Family, and Friends, to have a plan just incase. 2020 the year of be a good Neighbor hopefully.

    1. It is a terrible disaster that in my opinion isn’t getting nearly enough press time. Iowa disaster response was not nearly prepared for this scale of destruction. Alliant Energy says it needs to replace 2,500 damaged utility poles (something that normally would take 8 months). The amount of damage may exceed $4 billion.
      The pandemic has interrupted many supply chains. Economic recovery across the country AND supply chains is still unsure. If the Trump Administration continues to foment a cold war with China we can expect supply chains to be delayed. How many years has it been since we bought anything that didn’t say “Made in China” on the box?

      1. This was no normal derecho was it Jody? Years ago, I went through an event in Columbus, Wisconsin that was 90- 105mph roughly for 15 minutes. Devastated the city in seriously epic ways. Cedar Rapids tooks sustained winds category 3 hurricane strength for almost an hour. It’s hard to imagine this damage path. Seneca S.C took an almost mile wide EF-3 top end nighttime 160mph tornado this Spring. They got up and running much faster than Cedar Rapids. The city was totally wrecked badly, but nothing compared to what Cedar Rapids is trying to dig out of. Just terrible! 🙁

  7. Thanks Dr. Jeff Masters for this update. Looks like the prediction of an active season is well on its way.

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