NWS: Less than 1 percent probability of Category 5
The CNMI should expect to see more tropical cyclone activity than in 2016 and 2017, but not quite as much activity as in 2015 when typhoons Dolphin and Soudelor ravaged the islands, according to a coordinated assessment by the National Weather Service and Pacific ENSO Applications Climate Center.
The assessment for the rest of 2018 is based on independent Pacific-wide typhoon predictions, an internal forecast scheme designed by forecaster Paul Stanko for Micronesia activity, the current and predicted states of the El Nino-Southern Oscillation climate pattern, and the historical tropical cyclone activity associated with past ENSO states.
It is prepared for the CNMI government and citizens, and it is an update on the forecasts provided in April. These predictions could change over the next few months.
In detail, the weather assessment predicted the following:
• The Northern Islands could get a tropical storm or weak typhoon in late July or early August into September.
• Saipan and Tinian could see a nearby tropical storm in July and could be impacted by a typhoon in October, November, or December.
• Rota could see a nearby tropical storm or typhoon in July, but could be impacted by a typhoon in late October, November, December, and/or early January.
• For the remainder of the year, there is a 50 percent chance of getting a strong tropical storm (sustained winds of 50-73 mph) and a 25 percent chance of getting a Category 1 typhoon (sustained winds of 74-95 mph). The chance of a Category 2 typhoon (sustained winds of 96-110 mph) is about 15 percent, while the chance of a Category 3 typhoon (sustained winds of 111-129 mph) is around 10 percent. Chances of a Category 4 typhoon (sustained winds of 130-155 mph ) is around 3 percent, and finally, the chances of a Category 5 (sustained winds of 156-195 mph) is less than 1 percent. These percentages will likely need to be fine-tuned as the season evolves. Tropical cyclone activity for the CNMI could begin a little late, toward mid-summer, but keep in mind that the weather patterns can change quite rapidly. Remember, we are in the only basin that can get a typhoon any month of year.
• A move toward El Niño will continue to decrease the sea level heights, exposing the reefs to more direct sun during low tides and increasing chances for coral bleaching.
• Above normal rainfall should continue through the end of the year.
The National Weather Service and PEACC, however, reminded the public that these predictions can change as the year progresses.
NWS and PEACC said for Micronesia, there is a relatively predictable relationship between tropical cyclone activity and the state of El Nino-Southern Oscillation or ENSO. In the tropics, tropical cyclones generally move from southeast to northwest. Thus, if a tropical storm or typhoon develops southeast of the CNMI islands, it will often track toward the islands. If a tropical storm or typhoon develops west or north of the islands, it will usually move away from the islands. When an El Niño occurs, tropical storms and typhoons begin to develop earlier in the year and farther to the east toward eastern Micronesia. They tend to move toward the west, west-northwest or northwest, often toward the CNMI. When a La Nina event occurs, the storms tend to develop later in the year and west of or near the Mariana Islands. In this case, they usually move west before significantly intensifying. During El Niño events, the chance of Rota, Tinian, or Saipan getting direct hit triples when compared to the chance during non-El Niño periods. During an ENSO-neutral state, which is the transition state between El Niño and La Niña, the chance of getting a direct hit by a tropical storm or typhoon is much better than during La Niña, but not as good as during El Niño. In general, the odds of Rota, Tinian or Saipan getting a typhoon is about 1 in 5 or 6 or about once every 5 or 6 years. In El Niño years, the odds are 1 in 3 or about once every 3 years, while in La Nina the odds drop to 1 in 10 or about once every 10 years.
NWS and PEACC said Micronesia is now in an ENSO-neutral status, having recently transitioned from a La Niña climate state.
What do we expect for the future? Most climate forecast models suggest that we will remain in an ENSO-neutral state until late summer or early fall and then transition to an El Niño. In this scenario, we don’t get many early season tropical cyclones. A late summer or early fall El Niño will either be a weak or moderate one or the precursor to a stronger one in 2019. It is too early to say which will occur with any confidence. The Climate Prediction Center just issued an El Niño Watch on June 14. (PR)