Saipan, Tinian, and Rota have an estimated 50-50 chance of being hit by a destructive typhoon by the end part of this year, according to Weather Forecast Office Guam meteorologist Charles “Chip” Guard.
Guard told Saipan Tribune in an email that the destructive typhoon would likely be a Category 1 (minimal typhoon), Category 2 (moderate typhoon), or Category 3 (strong typhoon).
He predicts the destructive typhoon to occur on Saipan and Tinian in September, October, or November, and on Rota in October, November, or December.
Guard said the three islands may also have one to two additional typhoon threats during the same period.
“Keep in mind that these predictions can change as the typhoon season progresses,” he said.
For the Northern Islands, Guard said that Agrihan, Pagan, or Alamagan will likely experience one direct hit from a typhoon and one near-miss in August or September.
For the entire CNMI, Guard said their best estimate is that there will be transition from ENSO-neutral to a weak El Niño in August. “The El Niño would most likely peak in December and phase out in the spring,” he said.
Guard's tropical storm and typhoon activity predictions for the CNMI are based on a coordinated assessment between the National Weather Service and the Pacific ENSO Applications Climate Center.
Guard said the assessment is based on independent Pacific-wide typhoon predictions, an in-house statistical typhoon study, and the current and predicted states of the El Niño-Southern Oscillation (ENSO) and the historical tropical cyclone activity associated with those ENSO states.
He stressed that these predictions could change over the next few months.
Guard said tropical cyclones generally want to 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 or north of the CNMI, it will move away from the islands,” he said.
When an El Niño occurs, Guard said, tropical storms and typhoons begin to develop farther to the east and then can move toward the islands.
When a La Niña event occurs, he said, these storms tend to develop west of the islands or near the islands, but move west before significantly intensifying.
“During El Niño events, the chance of Saipan, Rota, or Tinian getting a direct hit triples when compared to the chance during non-El Niño periods,” he said.
For the Northern Islands, Guard said the chance of getting a direct hit doubles.
“During the 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 a typhoon is much better than for La Niña, but not quite as good as for El Niño,” he said.
Guard said the CNMI is now in an ENSO-neutral state, having just come out of a La Niña a month or so ago.
For the future, Guard cited three expected options: to remain in the ENSO-neutral state, revert back to La Niña, or transition to El Niño.
He said most are in agreement that the CNMI will either remain in an ENSO-neutral state or transition to an El Niño state.
He said the El Niño is not likely to be strong and will most likely be weak or barely moderate. “This suggests that the typhoons that do develop and threaten the CNMI would be weaker than supertyphoon intensity,” he said.
Guard cited that there was a weak to moderate El Niño in 2009 when two supertyphoons-Choi-wan and Melor-hit Alamagan in a two-month period.
He said Melor actually threatened Saipan, but turned toward the Northern Islands a day before it would have arrived on Saipan.