NWS: More storm activity in coming months

The CNMI should expect more tropical cyclone activity in the coming months compared to 2016, but not to the degree of 2015 when Typhoon Soudelor ravaged Saipan, according to National Weather Service-Forecast Office Guam warning coordination meteriologist Charles “Chip” Guard.

Guard’s prediction is part of a coordinated National Weather Service and Pacific ENSO Applications Climate (PEAC) Center assessment for tropical storm and typhoon activity for the Commonwealth of the Northern Mariana Islands for 2017.

He said while Saipan and Tinian could experience a nearby tropical cyclone as early as July, it is more likely to happen in September, October, and November.

NWS, meanwhile, expects the Northern Islands could get a tropical storm or typhoon as early as July, but more likely in August and September, while Rota could see a nearby tropical cyclone as early as July, but more likely in October, November, and December.

Guard also said that people should keep in mind that these predictions can change as the year progresses.

This assessment is based on independent Pacific-wide typhoon predictions, a locally-developed in-house statistical typhoon study, the current and predicted states of the El-Nino—Southern Oscillation (ENSO) climate pattern and the historical tropical cyclone activity associated with the past ENSO states. It is prepared for the CNMI government and citizens. These predictions could change over the next several weeks or months.

The assessment also said that for Micronesia, there is a relatively predictable relationship between tropical cyclone activity and the state of ENSO.

In the tropics, tropical cyclones generally move from southeast to northwest. Thus, if a tropical storm or typhoon develops southeast of the CNMI, it will often track toward the islands. If a tropical storm or typhoon develops west to north of the islands, it will usually move away from the islands.

When an El Nino 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-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 move west before significantly intensifying.

During El-Nino events, the chance of Rota, Tinian, or Saipan getting a direct hit triples when compared to the chance during non-El-Nino periods. During an ENSO-neutral state, which is the transition state between El-Nino and La-Nina, the chance of getting a direct hit by a tropical storm or a typhoon is much better than during LA Nina, but not as good as during El Nino. In general , the odds of Rota, Tinian, or Saipan getting a typhoon is about 1 in 7 or about every seven years. In El Nino years, the odds are in 1 in 3 or about every three years, while in La Nina the odds drop to 1 in 10 or about every 10 years.

Guard said the CNMI is currently in an ENSO-neutral status, and have been so since the decay of the rather weak 2016 La Nina.

He added that most climate forecast models suggest that the CNMI will remain in an ENSO-neutral state until summer. Thereafter, the models trend toward an El Nino event.

The NWS assessment said at this point, there is about an equal chance that the CNMI will remain ENSO-neutral or transition to El-Nino. Computer forecast models are now more skillful than in the spring. By summer, they begin to show increased skill. At this point, most models are in agreement that we will remain in an ENSO-neutral state into summer, and the trend is toward a continued ENSO-neutral state or a weak El-Nino state by late summer or fall. In this scenario, the CNMI won’t get early season tropical cyclones, as has been the case. A late El Nino will either be a short-lived one or the precursor to a stronger one in 2018.