Typhoon Jelawat (2018)
Typhoon Jelawat, known in the Philippines as Tropical Storm Caloy, was a powerful typhoon that affected the Caroline Islands on March 2018. The third tropical storm and the first typhoon of the 2018 Pacific typhoon season, Jelawat originated as a tropical disturbance that affected the Federated States of Micronesia before organizing into a tropical depression on March 24. It was further upgraded to a tropical storm by the Japan Meteorological Agency the following day, receiving the name Jelawat. Drifting northward under the influence of a weak ridge, the storm remained unorganized while staying east of the Philippines. Upon shifting northeastward, Jelawat rapidly intensified on March 30 due to low vertical wind shear and substantial outflow, peaking as a Category 4-equivalent super typhoon. Immediately thereafter however, it began to quickly weaken amid a sharp increase of wind shear, falling below typhoon strength on March 31. The storm transitioned into a subtropical cyclone on April 1, and persisted until the next day. The tropical disturbance that later became Typhoon Jelawat flooded parts of the Federated States of Micronesia. Most of the impact occurred in Pohnpei, where a person was killed and another was injured. Infrastructure was critically damaged and many homes were flooded throughout the island. After Jelawat had dissipated, its remnants produced rip currents that claimed the life of a woman in Guam. These remnants flowed into an atmospheric river that extended to California, flooding areas of the U.S. state. Traffic was disrupted among the San Francisco Bay Area, resulting in three injuries and one death. In response to the disaster in the Federated States of Micronesia, the country received assistance from the United States. Meteorological history 

A tropical disturbance centered at Pohnpei was observed on March 16, 2018, with favorable upper-level dynamics triggering widespread thunderstorm activity, or convection, across the island along with Kosrae and nearby islands and atolls of the Federated States of Micronesia. The following day, nascent rainbands were revealed wrapping around the system's defined low-level circulation. By situating over low vertical wind shear and very warm sea surface temperatures, the tropical disturbance underwent further development. Sufficient divergence aloft along with poleward outflow also supported its development into a tropical depression, forcing the Joint Typhoon Warning Center (JTWC) to announce a Tropical Cyclone Formation Alert. An equatorial Rossby wave supplied humidity to the atmosphere, facilitating the process. Thunderstorms continued to flare over the partially-exposed center, with the bulk of it displaced to the north. By March 24, the system was marked as a tropical depression by the Japan Meteorological Agency (JMA). The JTWC followed suit shortly afterward, giving it the numeral identifier 03W, when the disturbance had maintained its persistent deep convection. The depression also possessed a strong channel for ventilation enhanced by the mid-latitude westerlies. The system subsequently intensified into a tropical storm on March 25, according to the JMA, receiving the name Jelawat. As a consequence of the aforementioned displacement and moderate shear, the storm struggled to organize throughout March 26. On March 27, its circulation was completely exposed during convective development over the northwest quadrant. Vertical shear was offsetted by the poleward outflow, allowing for additional intensification. Later that day, the tropical depression entered the area of warning responsibility of the Philippine Atmospheric, Geophysical, and  Astronomical  Services Administration, prompting the agency to assign the local name Caloy. On March 28, following the consolidation of convection and presence of banding features over all quadrants, the JTWC upgraded Jelawat to a tropical storm. Around that time, the system turned northward while located  northwest of Yap. Jelawat then exited the Phillipine Area of Responsibility, before intensifying into a severe tropical storm that same day. With the storm being by the western side of a weakening ridge, a central dense overcast was formed broadening over the center. An eye was indicated on microwave imaging shortly thereafter, and by March 29, it was detected on satellite imagery. Aided by warm waters, Jelawat continued to stockpile convection into the eye feature, leading the JTWC to upgrade Jelawat to a typhoon at 18:00 UTC, followed by the JMA six hours later. Shifting northeastward alongside a subtropical ridge, the storm underwent explosive intensification on March 30, powered by low shear and an excellent outflow channel, and exhibited a sharp  eye. By 12:00 UTC, Jelawat attained its peak intensity, with 10-minute sustained winds of  and the lowest barometric pressure of  assessed by the JMA, and 1-minute sustained winds of  estimated by the JTWC, leading the latter agency to classify Jelawat as a super typhoon. Despite the conducive conditions, Jelawat was approaching an area of high vertical wind shear. Wind shear associated with a subtropical jet accompanied the outflow channel, weakening the storm. By March 31, Jelawat's structure began to rapidly deteriorate as it was being sheared to the northeast. Convection was soon very disorganized, with the deepest of it constricted to the northeast of the center, while Jelawat was positioned approximately  west of Agrihan. Subsequent to all of its deep convection becoming sheared, Jelawat was downgraded to a tropical storm. On April 1, its ragged circulation embedded with a baroclinic zone during advection, resulting in Jelawat transitioning into a subtropical cyclone while passing north of Pagan. The system continued to persist until it was last observed on April 2, and dissipated by 12:00 UTC of that day. Effects

Micronesia and Palau 

A Special Weather Statement from the National Weather Service (NWS) office in Guam was released for Pohnpei and Kosrae due to the potential of flash floods and landslides, stating that the system had already produced almost  of rainfall over the islands. The precursor disturbance to Jelawat passed slowly through Pohnpei, yielding a total  of rainfall on parts of the island on March 16 and 17, resulting in flooding and 24 landslides; one of the landslides led to an injury and killed one person. The downpour along with high waves inundated and damaged roads. Eleven bridges and culverts were damaged. Throughout the events, a landslide warning and six flood statements were announced by the island's local Weather Service Office. A number of homes were flooded in every municipality on the island. Nearly 250 houses were either damaged or destroyed, and critical damage was done to infrastructure as a result of the heavy rainfall. The NWS instated a tropical storm warning for Kayangel and Koror of Palau and Ngulu of Yap State on March 25; the warning for Koror was soon canceled the next day by the National Emergency Management Office of Palau, as Jelawat's winds were toned down to , with gusts of . In addition,  of rain fell over Palau. Dangerous levels of sea and surf conditions were reported, though storm surge was not a threat to the island nation. Jelawat poured around  of rainfall upon Yap as the system passed to the south of it throughout March 24–29, keeping the island chain under the influence of its outer rainbands. Chuuk State also received heavy showers, causing minor flooding of roadways. Mariana Islands 
Northwest swells from Jelawat were expected to increase surf levels from  across the reefs of the Northern Mariana Islands, prompting the issuance of high surf advisories. A tropical storm warning was raised along Agrihan and Pagan, and was forecasted that Jelawat would pass  north of Agrihan. The high surf advisories across the archipelago were lifted, when Jelawat was rapidly weakening from vertical wind shear, and no longer posed a threat towards the islands. Remnants of Jelawat produced surfs of  off Saipan and  off Ritidian Point. Nevertheless, no damage from the effects of Jelawat was reported in the Northern Mariana Islands. On April 3, a woman in Guam drowned after strong surfs combined with rip currents stranded her in water, and was later pronounced dead after being rescued along with two other swimmers. California 

Around early April, Jelawat's remnants entered an atmospheric river originating from Hawaii, dubbed a Pineapple Express, after its moist core flowed into the western end of the channel, reaching California. In response, flood warnings and watches were in effect for the Sierra Nevada, the Santa Cruz Mountains, and other areas of the state. The Yosemite National Park was closed down as a precaution. 147 flights at San Francisco International Airport were canceled due to the water supply, whereas nearly 400 were either delayed or canceled. The opener between the San Francisco Giants and Los Angeles Dodgers was rained out. Oroville Dam was monitored by the Department of Water Resources, though by the end of the heavy rain, the department did not need to utilize a partially rebuilt spillway, which was destroyed back in February 2017, and led to a crisis. The Merced River rose  above flood stage, flooding campgrounds and also meadows and roadways. Flooding also occurred along the Truckee River near Lake Tahoe. Towns nearby the Russian River experienced nearly  of rain. A traffic accident in Highway 4 in Pittsburg injured two people. Inundation, landslides, and erosions caused roads at Sonoma County to be closed, which had downed trees and power lines. Two people along with a dog were rescued from a car that was washed out on a flooded road. About 30 traffic accidents took place through Highway 101 in the county, although no one was seriously injured. At Sonoma Valley, a power outage affected customers of the Pacific Gas and Electric Company, though the utility stated that it had extra crews in seven Bay Area counties to respond to the power disruption. At Bodega Bay,  of rainfall was recorded in a day, more than the total rainfall of last month. A power outage was reported in Walnut Creek. In Highway 17 between Los Gatos and Altamont, about ten traffic accidents were reported, although it only caused one minor injury. Another incident in Highway 4 was reported when a truck spun out on eastbound Port Chicago, closing three lanes of traffic, entangling the East Bay freeway. In Grizzly Peak Boulevard, an emergency crew was called when a car fell  into an embankment; their efforts were hindered by fog alongside rain and wind. A woman, who was previously reported missing, was found dead near the vehicle about  down a hill. Aftermath 
Governor of Pohnpei Marcelo Peterson declared a state of emergency, and president of the Federated States of Micronesia Peter M. Christian issued a disaster declaration around mid-March 2018, releasing $50,000 from the country's Disaster Assistance Emergency Fund. On May 6, a declaration from the U.S. ambassador to FSM, Robert A. Riley III, allowed the Federal Emergency Management Agency (FEMA) and United States Agency for International Development (USAID) to assign a damage assessment across the FSM. Through the Compact of Free Association between the national governments, U.S. President Donald Trump issued a disaster declaration on July 20, and released funds for emergency relief and reconstruction assistance, after Christian requested a disaster declaration on June 13. USAID's Bureau for Humanitarian Assistance assisted in agriculture rehabilitation, whereas the USAID division in the Philippines supported the repair of the damaged homes as well as infrastructure and utilities. Relief and reconstruction funding from USAID totaled nearly $4.5 million. See also 

 Weather of 2018
 Tropical cyclones in 2018
 Other storms named Jelawat
 Other storms named Caloy
 Typhoon Bess (1979) – A typhoon that took a similar path and also formed in the month of March
 Typhoon Mitag (2002) – The first super typhoon on record in March
 Typhoon Dolphin (2015) – A typhoon which also affected Pohnpei early in its life
 Typhoon Wutip (2019) – The most powerful February typhoon on record

References

External links 

 03W.JELAWAT from the U.S. Naval Research Laboratory
 General Information of Typhoon Jelawat (1803) from Digital Typhoon
 JMA Best Track Data of Typhoon Jelawat (1803) (in Japanese)
 JMA Best Track (Graphics) of Typhoon Jelawat (1803)

Tropical cyclones in 2018
2018 Pacific typhoon season
Typhoons in Guam
Typhoons in the Federated States of Micronesia
Typhoons in the Northern Mariana Islands