At Least Three Named Storms Will Affect Parts of the U.S. This Week
All Client Alert
September 9, 2018
Source: The Weather Channel
Guam Governor Emergency Declaration ZIP Code List (reported by FEMA 9/9/18)
Northern Mariana Islands Governor Declaration ZIP Code List (reported by FEMA 9/9/18)
Guam Homeland Security (JIC Release No. 9 – Tropical Storm Update: Governor Declares Guam in COR3; Residents Urged to Continue to Prepare)
A rare configuration in the tropics may lead to three or four tropical cyclones affecting parts of the United States and its territories this week. The scope of these potential threats extends from the western Pacific to the Caribbean to the U.S. East Coast.
The systems are:
- Tropical Storm Florence, located in the middle of the North Atlantic on Sunday morning. Florence is expected to restrengthen into a major hurricane, and there is an increasing chance it will reach the U.S. East Coast later this week.
- Hurricane Olivia, hundreds of miles east of Honolulu, Hawaii. Still a Category 1 hurricane on Sunday morning, Olivia has been weakening, and that trend is expected to continue. However, Olivia will continue moving to the west or west-southwest and is predicted to be near the island chain around Wednesday as a tropical storm.
- A typhoon in the western Pacific called Mangkhut. Computer models agree Mangkhut will be approaching Guam, perhaps as a Category 3 equivalent or stronger, on Monday local time.
- Isaac in the tropical Atlantic is expected to approach the eastern Caribbean as a hurricane late week. It is possible this system could affect the U.S. Virgin Islands and Puerto Rico.
Eric Blake of the National Hurricane Center points out on Twitter how unusual it is to have so many far-flung threats to U.S. territory from tropical cyclones in a short period.
Each of these 1992 storms was a major landfall.
- Hurricane Andrew plowed into Florida just south of Miami as a Category 5 storm on Aug. 24. Damage was catastrophic, totaling some $27 billion (1992 USD), and 65 direct and indirect deaths were reported. Andrew’s strength at landfall was upgraded from Category 4 to 5 after an expert review in 2004.
- Typhoon Omar struck the U.S. territory of Guam as a Category 3 storm on Aug. 28. Omar destroyed some 2,000 homes on Guam, injured more than 200 people, inflicted $457 million in damage (1992 USD), and dropped 20.44 inches of rain on the National Weather Service office.
- Hurricane Iniki struck the Hawaiian island of Kauai as a Category 4 storm on Sept. 11. Iniki was the strongest hurricane by far known to make landfall on Hawaii. Iniki was also Hawaii’s most damaging hurricane on record, with some 1,400 homes destroyed and damages totaling $3.1 billion (1992 USD). Six deaths were reported.
This Week’s Threats: A Variety of Confidence Levels
Among the possible threats this week, there is very high confidence that Olivia will be approaching Hawaii around Wednesday, but the hurricane will be weakening and will likely be a tropical storm by that point. Only two hurricanes and two tropical storms have made landfall on Hawaii in at least the last 60 years, according to NOAA.
There is increasing confidence that Florence will affect the U.S. East Coast as a powerful hurricane by the latter part of this week.
Typhoon Mangkhut will pass near Guam starting Monday where a typhoon warning is in effect.
Isaac is forecast to move into the Lesser Antilles late this week as a hurricane. It’s uncertain what, if any, impacts Isaac may have on Puerto Rico and the Virgin Islands.
How Can There Be So Many Strong Storms in So Many Places?
The usual pattern during the Northern Hemisphere hurricane season is for one part of the tropics to be more active while another part is more quiet. For example, El Niño years tend to produce greater tropical activity in the northeast Pacific and less in the Atlantic, with the opposite holding true for La Niña years.
Another factor is the Madden-Julian Oscillation, which features a large zone of rising motion that straddles the equator and circles the globe about every 40 to 60 days. When the MJO is positioned to favor rising motion and hurricane development in the Pacific, it is typically suppressing activity in the Atlantic, and vice versa.
Because of these factors, it’s unusual to have active periods simultaneously over the Atlantic as well as the Northeast, Central, and Northwest Pacific. However, it is still possible for a strong hurricane to develop even where El Niño/La Niña or the MJO are in an unfavorable state.
Currently, the tropical Pacific is neutral (neither El Niño nor La Niña are in place), and the MJO is relatively weak. This may be helping to pave the way to see major storms across the Pacific and Atlantic at the same time.
Another element that supports widespread tropical activity is warm ocean temperatures, especially those above 80 degrees Fahrenheit. Sea surface temperatures are currently above average across large parts of the Northern Hemisphere tropics and subtropics.
Part of this week’s remarkable coincidence is also simply bad geographic luck. Guam, Hawaii, Puerto Rico, and the U.S. Virgin Islands are all small islands, dwarfed by the size of surrounding oceans, so the odds of a hurricane or typhoon affecting each of them within days are exceptionally low.
The Weather Channel issued a report outlining accelerated tropical storm activity in the Pacific and Atlantic oceans.