 This week, four tropical systems located in the western and eastern Pacific, will encounter the Fujiwhara effect. The Fujiwhara effect Is named after a Japanese researcher, Dr. Fujiwhara, after he performed various experiments on water vortices in the 1920’s. He concluded that when two cyclones come within 900 miles of each other, they will occasionally rotate cyclonically (counter-clockwise) around one another. As they rotate around, the two cyclones will sometimes have a tendency to merge together. The process will end when: “there is a stronger influence of a large-scale weather system from outside, one of the tropical cyclones weakens or the two cyclones merge” (Hong Kong Observatory).
In the eastern Pacific, Hurricane Hilary and Tropical Storm Irwin will begin to rotate around one another. Since Hilary is the larger storm, Irwin will be absorbed by Hilary after encountering the Fujiwhara effect. Southern California will feel some effects as the two systems will bring high surf and rip currents to the coast. In the western Pacific, Typhoon Noru and Tropical Storm Kulap will also experience the Fujiwhara effect. In this case, Typhoon Noru is the larger storm and Tropical Storm Kulap will be absorbed. While the event in the western Pacific doesn’t pose any threat to land, forecasters cannot rule out a possible land impact to the Japanese coast. The Fujiwhara effect is not rare, however, it is rare for two events within the same week to happen. Stay tuned for more in the tropics here! ⓒ 2017 Meteorologist Brandie Cantrell
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 DISCUSSION: Dunion et al. (2014) used IR satellite data to show that tropical cyclones tend to have a blowup of convection (cold cloud tops) near their center around sunset that subsequently propagates outward over the course of the following day. IR satellite data is sensitive primarily to cloud top. We wanted to see if this diurnal cycle was also present through a deeper layer of the storm's clouds below cloud top. Hence, in Leppert and Cecil (2016), we used active and passive microwave satellite data that can observe below cloud top to find that, indeed, this tropical cyclone diurnal cycle in cloud cover/rainfall extends through a deep layer. In the figure above, the top-left shows a snapshot of IR satellite data over Hurricane Hilary valid 0300 LST 24 July 2017. You can see cold cloud tops over the center of the storm and areas of cold cloud tops almost in a ring a little farther out from the center. The top-right shows the difference in IR brightness temperatures between the time of the image in the top-left and 6 hours prior showing the change in brightness temperature with time. The yellow-orange-red ring shows cooling brightness temperatures with time or the outward propagating diurnal pulse which corresponds with the ring of cold brightness temperatures in the top-left image. The bottom of the image show the expected radial location of this diurnal pulse as a function of time.
What is remarkable is that this diurnal pulse shows up consistently in storm after storm and in tropical cyclones around the world. Similar figures to that above can be found here for current storms. This feature seems really interesting, but we are not really sure its importance at this time. There is some indication that the blowup of convection is related to a similar increase in intensity. This diurnal cycle may also be related to changes in storm size. But, more research is needed to understand the importance of this tropical cyclone diurnal cycle. To learn more about other tropical cyclone-related stories from around the world, be sure to click here! ⓒ 2017 Meteorologist Dr. Ken Leppert II  DISCUSSION: “July, Stand By!” That phrase was part of an Old Mariner’s Poem that was first published in 1898, that refers to the aggressive time frame of the hurricane season. The “aggressive time frame” is when the Cape Verde Storms develop in the far eastern Atlantic (usually near the Cape Verde Islands). Even though the hurricane season officially runs from June 1 through November 30, the “aggressive time frame” usually lasts from early August to late September, but can start as early as mid-July and last as late as early October.
These Eastern Atlantic Tropical Cyclones can easily because the strongest ones of the season, averaging 1 or 2 major hurricanes a year! For Florida residents, Hurricane Andrew of 1992, Hurricanes Frances and Jeanne both of 2004, are an example of those aggressive time frame hurricanes. These hurricanes were so infamous, their names have been retired, and their memories have been etched in the minds of Floridians for years to come. Oh, by the way, if you are interested in the rest of the poem, here it is: “June, Too Soon. July, Stand By! August, Look Out You Must. September, Remember. October, All Over”. So for all you hurricane enthusiasts out there, Stand By! Those strong Cape Verde Tropical Cyclones may be here before you know it. To learn more about other tropical cyclone-related stories from around the world, be sure to click here! ⓒ 2017 Meteorologist Michael Leiba Analyzing Hurricane Fernanda At and Around Peak Intensity (credit: GOES-R Advanced Baseline Imager)7/17/2017  DISCUSSION: Over the past 5 to 6 days, the world has watched the Eastern Pacific Ocean heat up in terms of the collective tropical cyclone activity. The biggest story in this recent bout of tropical cyclone activity was the fairly swift intensification of Hurricane Fernanda. Moreover, during the majority of this period of time, Hurricane Fernanda managed to maintain an almost perfectly symmetric eyewall and overall storm relative outflow. Hence, it maintained its status as a powerful and symmetric tropical cyclone which had the potential to deliver major impacts to parts of western North America or small islands just offshore from western North America. However, Fernanda ultimately took a track which positioned it much further offshore (i.e., over the open waters of the Eastern Pacific Ocean) and mitigated any land-based threats. To see the full loop shown in the video briefing above, click on the following link.
To learn more about other tropical cyclone-based events occurring from around the world, be sure to click here! ©2017 Meteorologist Jordan Rabinowitz  Tropical Storm Don is located east-southeast of the Windward Islands with maximum sustained winds near 45 mph. Currently, the system is over warm waters and a low-level shear environment which may result in some strengthening. Once the system enters the eastern Caribbean Sea, however, strong low-level easterly flow accompanied with strong upper-level westerly flow will diminish Don. The National Hurricane Center is forecasting the lifespan of Don to be 72 hours. Tropical Storm warnings have been issued for Grenada as conditions are expected to deteriorate within the next 24 to 36 hours. Tropical Storm watches have been issued for Barbados, St. Lucia, St. Vincent and the Grenadines. Rainfall amounts up to 4 inches are possible in the Windward Islands through Wednesday morning. Tropical-storm-force winds are to be expected in Grenada on Tuesday. The next advisory will be 11:00 PM AST.
Stay up-to-date on the tropics here! ⓒ 2017 Meteorologist Brandie Cantrell  As Major Hurricane Fernanda continues to churn over open ocean, the forecast suggests a weakening trend. Currently, Fernanda has maximum sustained winds near 125 mph (Category 3 hurricane on the Saffir-Simpson Scale), and is headed west-northwest at nearly 9 mph. Hurricane-force winds extend outward up to 30 miles from the center, and tropical-storm-force winds extend outward up to 115 miles from the center of the storm. As Fernanda nears Hawaii, vertical shear should weaken the system even further as the forward motion decreases. The entire Forecast Discussion is as follows:
Although the central convection has eroded slightly, Fernanda remains a well-organized tropical cyclone. The upper-level outflow is well defined over most of the circulation and the cloud pattern remains quite symmetric in appearance. The current intensity estimate remains 110 kt, which is a blend of the various subjective and objective Dvorak estimates. Since Fernanda will be traversing decreasing sea surface temperatures, gradual weakening is likely during the next couple of days. Later in the forecast period, vertical shear, associated with a large upper-level trough near the Hawaiian Islands, should result in more rapid weakening. The official intensity forecast is very close to the model consensus. The motion is bending slightly to the right and slowing. The mid-level ridge to the north of Fernanda is forecast to weaken over the next couple of days. This should cause a turn toward the northwest with a little more slowing in forward speed over the next 48 hours. Later in the forecast period, a more leftward heading is likely while the ridge rebuilds somewhat. The official forecast track is only slightly north of the previous one and is close to the model consensus, TVCN. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 14.1N 131.6W 110 KT 125 MPH 12H 18/0600Z 14.8N 132.6W 100 KT 115 MPH 24H 18/1800Z 15.7N 133.7W 90 KT 105 MPH 36H 19/0600Z 16.5N 134.8W 80 KT 90 MPH 48H 19/1800Z 17.1N 136.0W 70 KT 80 MPH 72H 20/1800Z 17.9N 139.1W 50 KT 60 MPH 96H 21/1800Z 18.3N 142.5W 35 KT 40 MPH 120H 22/1800Z 18.8N 145.0W 25 KT 30 MPH...POST-TROP/REMNT LOW As for Tropical Depression Seven-E, the maximum sustained winds are near 35 mph, and is expected to near tropical storm intensity. However, southwesterly shear will help diminish the system by day 5. Stayed tuned for more updates as we head into the peak of hurricane season here! ⓒ 2017 Meteorologist Brandie Cantrell  Tropical Storm Fernanda has been upgraded to a hurricane by the National Hurricane Center at the 2:00 PM PDT advisory. Currently, Hurricane Fernanda has maximum sustained winds of 80 mph and is still rapidly intensifying. Fernanda is staying on a westward track moving 12 mph in the Pacific Ocean. Hurricane-force winds extend outward of 15 miles from the center of the storm, and tropical-storm-force winds extend outward of 60 miles from the center. Forecasters are expecting Hurricane Fernanda to strengthen to a major hurricane by tomorrow evening. The forecasted positions and max winds issued by the National Hurricane Center is as follows:
FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 11.2N 116.0W 70 KT 80 MPH 12H 14/0600Z 11.1N 117.5W 85 KT 100 MPH 24H 14/1800Z 10.9N 119.4W 100 KT 115 MPH 36H 15/0600Z 10.9N 121.3W 115 KT 130 MPH 48H 15/1800Z 11.3N 123.5W 120 KT 140 MPH 72H 16/1800Z 12.5N 128.0W 125 KT 145 MPH 96H 17/1800Z 14.0N 132.5W 115 KT 130 MPH 120H 18/1800Z 15.5N 136.0W 95 KT 110 MPH The next advisory will be issued around 8:00 PM Pacific Daylight Time. Stay updated on the tropics here! ⓒ 2017 Meteorologist Brandie Cantrell Tropical Storm Fernanda to Strengthen to a Hurricane! (Photo Credit: National Hurricane Center)7/13/2017  Tropical Storm Fernanda is located about 845 miles southwest of Baja, California moving west at 12 miles per hour. As of the 8:00 AM advisory issued by the National Hurricane Center in Miami, Florida, Fernanda has maximum sustained winds of 65 miles per hour and extend outward of about 45 miles from the center of the storm. Strengthening is expected over the next 48 hours as it is forecasted to become a hurricane later today. Models continue to show strengthening into a major hurricane by tomorrow evening (category 3 or higher). After 48 hours, the storm is projected to move into cooler sea temperatures which could cause slight weakening. The forecast discussion, as well as the forecasted winds over the next couple of days, is as follows:
Recent IR and WV images show that Fernanda has begun to establish good outflow in all quadrants, indicating that the shear that previously affected the tropical storm is diminishing. Recent SSMI and SSMIS passes from 1016 and 1130 UTC, respectively, show that that convection is wrapping all the way around a mid-level center, but the low-level center remains displaced a little to the north-northeast. Dvorak estimates from TAFB and SAB have increased to T 3.5 / 55kt, and the initial intensity has been increased to that value. Confirming what the satellite data suggests, the analyzed shear has decreased below 10 kt. Warm SSTs and sufficient moisture are also contributing to an environment that is very conducive for continued intensification. The SHIPS-RII shows a greater than 50 percent chance of a 30 kt increase in 24 hours and a 45 kt increase in 48 hours. This is a notable increase in the probabilities which have doubled in the last 12 h. Considering the convective structure of the cyclone has improved over the past few hours, and the lack of any obvious inhibiting environmental factors, rapid intensification within the next 24 or 36 hours seems likely. The intensity forecast has been substantially increased for the first 48 hours and now explicitly shows an increase of 30 kt within 24 hours. Fernanda is forecast to be at or near major hurricane strength by tomorrow evening, with conditions favoring additional intensification after that. Near the end of the forecast period, the hurricane is expected to encounter decreasing sea surface temperatures that could cause slight weakening. The intensity forecast is near the top of the guidance envelope, close to the corrected consensus aids FSSE and HCCA. No major changes have been made to the track forecast. The initial motion estimate remains 265/9 kt. A deep-layer ridge extending over a large portion of the eastern north Pacific will steer Fernanda generally westward for the next 2-3 days. Most of the dynamical guidance still shows a slight weakening of the ridge after about 3 days which would cause Fernanda to turn toward the northwest. The NHC forecast is very close to to the track consensus TVCN and is nearly on top of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 11.7N 115.0W 55 KT 65 MPH 12H 14/0000Z 11.5N 116.4W 65 KT 75 MPH 24H 14/1200Z 11.2N 118.3W 85 KT 100 MPH 36H 15/0000Z 11.0N 120.3W 100 KT 115 MPH 48H 15/1200Z 11.2N 122.4W 110 KT 125 MPH 72H 16/1200Z 12.0N 126.9W 120 KT 140 MPH 96H 17/1200Z 13.4N 131.0W 115 KT 130 MPH 120H 18/1200Z 15.0N 135.5W 105 KT 120 MPH The next advisory will be issued around 2:00 PM Pacific Daylight Time. Stay tuned for up-to-date information on the tropics here! ⓒ 2017 Meteorologist Brandie Cantrell  Tropical Storm Eugene continues to churn off of the west coast of Mexico. As you can see from the graphic above, Eugene will continue to the northwest and is expected to weaken into a remnant low in the next 24-48 hours. As of the 8:00 AM advisory issued by the National Hurricane Center, Tropical Storm Eugene has maximum sustained winds of 50 mph and is moving 10 mph to the northwest. The NHC noted that even though the center is off shore, there are still impacts to the coast of southern California. The storm will continue to bring high surf and dangerous rip currents to Baja, California as it moves northwestward. Eugene is expected to dissipate completely within the next 5 days. The official 8:00 AM advisory issued by the National Hurricane Center is as follows:
Deep convection associated with Eugene is diminishing in depth and areal coverage. Consequently, subjective Dvorak estimates from SAB and TAFB as well as objective ADT values from CIMSS continue to drop. The initial intensity is set at 45 kt, though this is with a substantial amount of uncertainty. A 0949Z AMSR2 microwave image helped to locate the center of Eugene this morning. The system is moving toward the northwest at about 9 kt. Eugene is expected to continue moving in the same direction and speed for the next couple of days, as it is rounding the southwestern portion of a mid-level subtropical ridge. The official track forecast is nearly unchanged and continues to be based upon the multi-model consensus technique TVCN. Eugene has been weakening due to ingestion of cool and dry air as it moves into the stratocumulus-infested waters west of Baja California. This will continue due to the northwestward track over even cooler SSTs during the next two days. It is expected that Eugene will lose its deep convection and become a remnant low in 24-36 hr and dissipate completely in about 5 days. The official intensity forecast is slightly lower than that previously and is based upon the multi-model consensus technique IVCN. Swells generated by Eugene will continue to propagate northward along the west coast of the Baja California peninsula to southern California during the next couple days, causing high surf and dangerous rip current conditions. Please refer to statements issued by your local weather office for additional information. To stay updated on the tropics, click here! ⓒ 2017 Meteorologist Brandie Cantrell |
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