Gamma satellite image
Infrared satellite image of Tropical Storm Gamma over the Caribbean at 11:30 a.m. EDT October 3, 2020. (Image credit: RAMMB/CIRA/Colorado State University)

An intensifying Tropical Storm Gamma was barreling ashore in Mexico’s Yucatan Peninsula early Saturday afternoon with top winds of 70 mph, just below hurricane strength. Gamma was bringing heavy rains in excess of an inch per hour to portions of the Yucatan Peninsula on Saturday, and flash flooding from these torrential rains is the greatest threat from the storm. Some 24-hour rainfall amounts from Gamma at Weather Underground personal weather stations as of noon EDT Saturday included:

Puerto Morelos, Mexico: 15 inches
Cozumel, Mexico: 11.15 inches
Cancun, Mexico: 5.64 inches
Roatan, Honduras: 4.79 inches

The 2020 parade of record-early named storms continues

Gamma developed into a tropical storm on Friday evening, and its October 2 arrival marked the earliest date that any Atlantic season has produced its 24th tropical storm, topping the record held by Beta from October 27, 2005.

With the Atlantic hurricane season three-quarters done, we’ve already had 24 named storms, eight hurricanes, two intense hurricanes, and an accumulated cyclone energy (ACE) index of 106 (24% above average for the date). Only one Atlantic hurricane season since 1851 has had more named storms during an entire season: 2005, with 28 named storms. According to Colorado State University hurricane scientist Phil Klotzbach, the averages for this point in the season are nine named storms, five hurricanes, two intense hurricanes, and an ACE index of 85.

Gamma’s landfall in Mexico gives the “Greek” storms of 2020 three consecutive landfalls, along with Alpha in Portugal and Beta in Texas. The only other year with Greek-named storms, 2005, also had three of these late-season storms make landfall: Alpha, Beta, and Gamma, all in the Caribbean.

Figure 1. Track forecasts out to eight days for Tropical Storm Gamma from the 6Z (2 a.m. EDT) Saturday, October 3, run of the new version of the GFS ensemble model (GEFS). The black line is the mean of the 31 ensemble members; individual ensemble member forecasts are the thin lines, color-coded by the central pressure they predict for Gamma. The long-range forecasts predominately call for a weak storm with a pressure greater than 1000 mb (green and blue colors). (Image credit: Tropical Tidbits)

Forecast for Gamma

Conditions for development were less favorable on Saturday than on Friday, with wind shear a moderately high 15-20 knots and a drier atmosphere (a mid-level relative humidity near 60%). Despite these factors, satellite images showed that Gamma continued to grow more organized right up until landfall, with an eye beginning to appear.

The trough of low pressure pulling Gamma to the northwest is expected to move eastwards on Sunday and leave the storm behind, putting Gamma in an area of weak steering currents. As a result, Gamma’s forward motion is expected to slow to less than 5 mph Saturday night through Monday, resulting in very heavy rains across much of Mexico’s Yucatan Peninsula, portions of Central America, and western Cuba. The current model consensus is that a weak ridge of high pressure will build to the north of Gamma on Sunday and Monday, forcing the storm to move west or west-southwest Monday through Wednesday.

Conditions for development of Gamma will become more hostile on Sunday and Monday, when high wind shear of 20-30 knots and dry air over the Gulf of Mexico will interfere with development, as will land interaction with the Yucatan Peninsula. Because of these obstacles, the top intensity models generally show weakening of Gamma over the next five days.

Figure 2. Rainfall outlook (in inches) for the two-day period from 2 a.m. EDT (6Z) Saturday, October 3, 2020, through 2 a.m. EDT Monday, October 5, from the 6Z Saturday, October 3, run of the GFS model. The model predicted rainfall amounts in excess of 12 inches (yellow-orange colors) for portions of Mexico from Gamma. (Image credit: Tropical Tidbits)

Central Caribbean tropical wave 92L may develop

Further complications on predicting Gamma’s track may arise by Monday or Tuesday as another tropical wave, now moving through the central Caribbean, arrives in the western Caribbean and potentially develops into a tropical depression or tropical storm. This wave, which was designated 92L by NHC on Saturday morning, was located south of Haiti on Saturday afternoon and was moving west-northwest at about 10 mph. Satellite images showed the wave had a modest amount of heavy thunderstorms that were poorly organized and the wave was under a moderate 10-15 knots of wind shear, which was slowing development.

Also see: Bidding farewell to Dr. James McFadden, the longest-serving NOAA Hurricane Hunter

When 92L reaches the western Caribbean on Monday, the shear is expected to drop to a low 5-10 knots, ocean temperatures beneath its path will warm to 30 degrees Celsius (86°F), and 92L will be in a moist environment — conditions that favor development. The top three models for predicting tropical cyclone genesis were giving modest support for development to occur on Monday or Tuesday in the western Caribbean, and in an 8 a.m. EDT Saturday Tropical Weather Outlook, the National Hurricane Center gave 92L two-day and five-day odds of development of 20% and 50%, respectively.

There were two other areas of interest in the central Atlantic that were being given low odds of development by NHC on Saturday morning, but neither of these two systems are a threat to any land areas.

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Posted on October 3, 2020 (12:44pm EDT).

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...

33 replies on “Tropical Storm Gamma makes landfall in Mexico’s Yucatan Peninsula”

    The Flood Watch continues for
    * A portion of east central Florida, including the following areas,
      Coastal Volusia, Indian River, Inland Volusia, Martin, Northern
      Brevard, Northern Lake, Orange, Osceola, Seminole, Southern
      Brevard, Southern Lake and St. Lucie.
    * Through late tonight
    * Widespread showers and isolated lightning storms, some producing
      periods of heavy rain, will move across east-central Florida today
      into tonight. Widespread rainfall amounts of 2 to 3 inches are
      expected, with isolated higher amounts of 5 to 6 inches are
    Do not enter or cross flowing water or water of unknown depth.
    A Flood Watch means there is a potential for flooding based on
    current forecasts. You should monitor later forecasts and be alert
    for possible flood warnings. Those living in areas prone to flooding
    should be prepared to take action should flooding develop.
  2. Morning everyone….we have some conflicting steering winds for Gamma right now which is causing the stand-off…..forecasted 21z 500mb level winds still favor a NNE pattern and the 850mb level winds favor a SW pattern….see attached for 500mb….

  3. bullpucky … is there a way to report this garbage? AFAIK Dems are behaving, I couldn’t say the same for JE.

  4. Tropical Weather Outlook
    NWS National Hurricane Center Miami FL
    800 PM EDT Sat Oct 3 2020
    For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
    The National Hurricane Center is issuing advisories on Tropical 
    Storm Gamma, located inland over the Yucatan Peninsula.
    1. A tropical wave located over the central Caribbean Sea is producing 
    an area of disorganized showers and thunderstorms.  Environmental 
    conditions are expected to become more conducive for development, 
    and a tropical depression is likely to form during the early or 
    middle portions of next week while the system moves westward or 
    west-northwestward at about 15 mph across the central and western 
    Caribbean Sea and then into the southern Gulf of Mexico.  Locally 
    heavy rainfall and gusty winds will be possible across portions of 
    Hispaniola, Jamaica, Cuba, and the Cayman Islands during the next 
    few days, and interests on those islands should monitor the progress 
    of this disturbance.
    * Formation chance through 48 hours...medium...40 percent.
    * Formation chance through 5 days...high...70 percent.
    2. Disorganized showers and thunderstorms continue in association with 
    a tropical wave located over the central tropical Atlantic.  Some 
    slow development of this system is possible during the next couple 
    of days while it moves west-northwestward or northwestward at 10 to 
    15 mph.  Significant development is not expected beyond that time 
    due to the system moving into a region of strong upper-level winds.
    * Formation chance through 48 hours...low...20 percent.
    * Formation chance through 5 days...low...20 percent.
    3. An area of disorganized showers and thunderstorms over the central 
    Atlantic more than 1000 miles east-southeast of Bermuda is 
    associated with a surface trough of low pressure.  This system 
    is expected to move toward the west-southwest at around 10 mph, 
    and some slow development is possible during the next couple of 
    days before it too encounters strong upper-level winds.
    * Formation chance through 48 hours...low...10 percent.
    * Formation chance through 5 days...low...10 percent.
    Forecaster Cangialosi
  5. With that tenuous, weird and wandering post-Yucatan path projection for Gamma, still hard to be certain of much about it, other than the likely weakening. If it does steer further west, given saturation from Laura and Beta, not good for central Gulf Coast.

  6.  Sat Oct 3 2020/
    This morning a jet streak was across north FL and south GA while
    mid level troughing stretched down the eastern states and into
    the Gulf of Mexico. Mid level ridging from the Atlantic extended
    across the Bahamas to Cuba. These features continue today with
    little change as they provide a very moist southwest to south flow
    aloft. At the surface the south moving front from yesterday
    stalled across central FL. It meanders there until this afternoon
    or evening when it merges with a north bound warm front exiting
    south FL. The combination of all these features result in
    considerable cloudiness and increasing rain chances spreading from
    the south today. Greatest rainfall is expected to be pushing in
    the area later tonight.
    The current forecast looks good although may make minor
    adjustments as needed throughout the day. Tropical Storm Gamma is
    approaching the east coast of the Yucatan peninsula this
    morning...details may be found in National Hurricane Center
    A couple of boundaries across the waters today merge later in the
    day...providing showers and a few thunderstorms for the next
    couple of days. Northeast winds prevail for the small
    craft exercise caution speeds today but diminishing some tonight.
    .Preliminary Point Temps/PoPs...
    TPA  71  78  69  83 /  80  70  40  30
    FMY  72  84  73  88 /  70  60  30  50
    GIF  69  80  69  84 /  70  70  30  40
    SRQ  72  81  72  85 /  80  60  40  40
    BKV  68  77  67  83 /  80  80  40  30
    SPG  72  77  71  82 /  80  70  40  30
  7. Tropical Storm Gamma Tropical Cyclone Update
    NWS National Hurricane Center Miami FL AL252020
    1200 PM CDT Sat Oct 03 2020


    Surface observations and satellite images indicate that the center
    of Tropical Storm Gamma made landfall in the northeast Yucatan
    Peninsula near Tulum, Mexico, around 1145 AM CDT. The storm was
    very close to hurricane strength at landfall, with maximum
    sustained winds near 70 MPH (110 MPH) with higher gusts.

    A weather station at Xel-Ha Park, along the Yucatan coast just
    north of Tulum, reported a sustained wind of 55 mph (89 km/h) and a
    gust to 68 mph (109 km/h) within the past hour.

    LOCATION…20.2N 87.5W

    Forecaster Pasch

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