Infrared satellite image
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.

GOES-16 satellite image
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
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
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.

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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, 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 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. An elongated area of low pressure, located a little over 1000 miles 
    east of the Windward Islands continues to produce a concentrated 
    area of showers and thunderstorms mainly on the west side of the 
    disturbance.  Environmental conditions are conducive for further 
    development, and a tropical depression is expected to form during 
    the next day or two while the system moves generally 
    west-northwestward at 15 to 20 mph across the central and western 
    portions of the tropical Atlantic.
    * Formation chance through 48 hours...high...90 percent.
    * Formation chance through 5 days...high...90 percent.

    From this morning’s TWD …. I think we can expect changes at 11 or 5 today on 98L

  2. the following statement might have slight translations errors

    The Central Meteorological Observatory continued to issue an orange typhoon warning at 06:00 on August 19:

    This year’s No. 7 typhoon “HIGOS” made landfall on the coast of Jinwan District, Zhuhai City, Guangdong Province at around 6 o’clock this morning (19AUG). The maximum wind force near the center was (35 m/s) and the lowest pressure at the time of landfall was 970 hPa,

    Typhoon “HIGOS” center is located at 22.1N 113.3E.

    It is expected that “HIGOS” will move to the northwest at a speed of about 20 km/h and will gradually weaken.

  3. Japan Meteorological Agency
    Tropical Cyclone Advisory #11 – 3:00 AM JST August 19 2020
    South China Sea

    At 18:00 PM UTC, Severe Tropical Storm Higos (996 hPa) located at 21.6N 113.8E has 10 minute sustained winds of 50 knots with gusts of 70 knots. The cyclone is reported as moving west northwest at 11 knots.

    Gale Force Winds
    100 nm from the center in eastern quadrant
    60 nm from the center in western quadrant

    Dvorak Intensity: T3.0

    Forecast and Intensity
    24 HRS: 23.8N 109.2E – Tropical Depression over land southern China

    1. China Meteorological Administration has Higos at a typhoon near the Guangdong province coastline

      WTPQ20 BABJ 182100
      TY HIGOS 2007 (2007) INITIAL TIME 182100 UTC

      00HR 21.8N 113.6E 970HPA 35M/S (70-75 knots)

  4. Afternoon all. Genevieve is very impressive at this hour … hopefully that NW track will verify and the worst effects will remain offshore.

    1. I assume they’ll close the comments eventually. Maybe in November, post season. There will be a half million comments by

  5. Florida needs to watch both 97L and 98L, not to mention whatever else pops up next week with more favorable conditions across the Atlantic!

  6. HERE we go again florida….. as usual more than 5 days out the models are showing 98l hitting florida… lmao.. the hype is already starting……. but as we all know 100’s of times this doesnt happen

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