Tag Archives: TS Cristobal

Steve Gregory on Current Tropical Conditions

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Hurricane CRISTOBAL Northbound – ‘97L’ Needs Monitoring – Strong System over Africa

By: SteveGregory , 4:01 PM GMT on August 26, 2014

HURRICANE CRISTOBAL

CRISTOBAL intensified into a hurricane early last night as wind shear eased a bit, and outflow improved somewhat to the North and south. Shear remains relatively high near 20Kts, and with no improvement in the outflow pattern above the storm expected and the proximity to drier to its west – significant intensification appears unlikely as the 988mb storm moves Northward during the next 2 days along the western periphery of the sub-tropical (Bermuda) High centered in the central Atlantic. All the models are now in excellent agreement on both the track and intensity forecast for CRISTOBAL, and except for large waves and localized rip currents along the east coast – CRISTOBAL will have no impact on the US mainland

INVEST 97L POSES A POTENTIAL THREAT OF DEVELOPMENT THIS WEEKEND

Although NHC dropped 97L overnight, this system is now BACK on the NHC home page chart, most likely due to several global models now forecasting it to develop this weekend as it approaches the Leeward Islands – with the GFS and a few other models tracking it as a cyclone into the southeast coast of the US mainland late next week. Because NHC ‘dropped’ the system over night, none of the specialized hurricane models we executed during the 12Z cycle run. However, the models will almost certainly be initialized for the 18Z cycle run later today. That said – the system is currently surrounded by dry and somewhat stable air with no significant outflow signature seen on SAT imagery at this time; so development, if any, will be quite slow for the next 72 hours.

STRONG DISTURBANCE STILL WESTBOUND OVER AFRICA

Finally, the strongest African tropical disturbance of the season is now located over west-central Africa with a long history of deep convection and a well established rotation in low to mid levels. The disturbance is now moving slowly westward, and is expected to emerge off the west African coast this weekend. Some model projections forecast this system to gradually intensify next week – but also put it on a more Northwesterly track next week – implying this system will start heading out to sea by later next week.

Fig 1: Early morning VIS imagery shows the center of CRISTOBAL on the NW side of deep convection moving Northward at about 5Kts (based on the last 6 hours of RECON/SAT image tracking). The overall satellite signature is highly unusual for a tropical cyclone, especially of hurricane intensity – with the system appearing to be along the southern edge of a mid-latitude frontal boundary. In some respects, that is exactly what has occurred over the last 24 hours, with the southward plunge of well defined dry air surge to the immediate west of the cyclone, leading to a ‘linear’ type orientation of convection extending from well north of CRISTOBAL southward to the storm itself. There is a small possibility that this ‘dynamic’ boundary actually helped intensify the cyclone, despite the moderate shear and dry air that is just west of the storms core circulation. Normally, dry air this close to a relatively weak and sheared system like we had would weaken or totally halt intensification – but in this case (the first I’ve ever seen) – the opposite occurred. It’s worth noting that the dry air surge extended into the northern GOM as well – triggering a line of strong convection there.

Fig 2: The above overview of the tropical Atlantic shows a significant tropical wave/disturbance that was (and now again, is) 97L approaching 50W, and is still westbound at ~16Kts. Dry air is to the north and northwest of the system does not appear to be infiltrating the central area of what isolated convection there is. However, the system still remains in a less than favorable area of somewhat stable air – with no upper level wind support. As the system approaches the far eastern CARIB late this week, the environment should become somewhat more favorable for development.

Fig 3: Enhanced IR imagery over Africa earlier this morning highlights the very strong system in west-central Africa. This system had been moving W/SW for the last 36 hours – but has slowed its forward motion somewhat, and is expected to move on a West/Northwest (290°) during the next few days.

Fig 4: The above image over Africa includes satellite derived winds – and show a well established cyclonic flow around the major system of interest – just as it had for the last 2 days

Fig 5: The global models like the NAVY GEM above – and the GFS & CMC forecasts (not shown) all forecast the system to slowly intensify next week, with the GFS then carrying the system into the SE U.S. coast as a cyclone. Clearly, this system needs close monitoring.

from:    http://www.wunderground.com/blog/SteveGregory/comment.html?entrynum=220

Dr. Masters on Tropical Storms

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Cristobal a Hurricane; Little Change to 97L

By: Dr. Jeff Masters , 12:25 PM GMT on August 26, 2014

It doesn’t look much like hurricane, but the Hurricane Hunters measured surface winds around 75 mph on Monday evening and Tuesday morning in Hurricane Cristobal, making it the third hurricane of the 2014 Atlantic hurricane season. These missions proved the value of hurricane hunter flights, since there is no way that we would have known Cristobal was a hurricane based on satellite data. The storm is stretched out in a long line of heavy thunderstorms, has no eye or low-level spiral bands, and is giving early August’s Hurricane Bertha some stiff competition for ugliest Atlantic hurricane of the century. Along with Hurricane Arthur and Hurricane Bertha, Cristobal gives us three Atlantic hurricanes so far this year, exceeding the entire 2013 Atlantic hurricane season total. The second (and final) hurricane of the 2013 season (Ingrid) did not arrive until September 14. On average, the third hurricane of the Atlantic season arrives on September 9, and the third named storm of the year on August 13. The last time the first three named storms in the Atlantic became hurricanes was in 1983, when Alicia, Barry and Chantal all became hurricanes (if we exclude 1992, when an unnamed subtropical storm formed prior to the arrival of Hurricanes Andrew, Bonnie, and Charley.) Cristobal continues to dump heavy rains over the Central and Southeast Bahamas and Turks and Caicos Islands as the storm heads northeastwards out to sea. Satellite loops show that Cristobal is struggling with wind shear, with a center of circulation partially exposed to view, and all the heavy thunderstorms pushed to the south and east sides of the center. The only land area at risk from Cristobal is Bermuda, and the 5 am EDT Tuesday Wind Probability Forecast from NHC gave that island a 27% chance of experiencing tropical storm force winds of 39+ mph. The GOES-14 satellite is in rapid-scan mode over Cristobal on Tuesday, and you can access an impressive 1-minute resolution satellite loop of the storm from the NOAA/RAMMB website.


Figure 1. MODIS true-color image showing Tropical Storm Cristobal’s intense thunderstorms stretching from the Southeast Bahamas to Bermuda at 2 pm EDT on August 25, 2014. At the time, Cristobal had top winds of 60 mph. Image credit: NASA.

Little change to 97L headed towards the Lesser Antilles
A tropical wave (Invest 97L) was near 13°N, 47°W on Tuesday morning, about 900 miles east of the Lesser Antilles Islands, and was headed west to west-northwest at about 15 mph. Satellite loops show the wave has changed little since Monday, and has a modest amount of spin but only a small amount of heavy thunderstorms. Water vapor satellite images and the Saharan Air Layer analysis show that 97L is located in a dry environment, which is keeping development slow. Wind shear was a moderate 10 – 20 knots, which should allow some slow development. Sea Surface Temperatures are near 27.5°C, which is warm enough to allow some slow development. The wave should arrive in the Lesser Antilles Islands by Friday and be near Puerto Rico on Saturday, according to the Tuesday morning runs of the GFS model. None of the three reliable computer models for predicting tropical storm formation predict 97L will develop over the next five days. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 0% and 20%, respectively. These odds are 10% lower than their previous advisory, and NHC has stopped running their suite of models on 97L.

New tropical wave coming off coast of Africa this weekend
A large and powerful tropical wave will move off the coast of Africa on Friday evening, and the GFS model has been very aggressive in recent runs about developing this wave into a tropical storm within a day of its emergence. The other reliable models for tropical cyclone genesis, the European and UKMET models, have not been developing this wave right away. Residents of the Cape Verde Islands should anticipate the possibility of heavy rain and strong winds on Saturday as the wave moves west at 10 – 15 mph across the islands. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 0% and 30%, respectively.

The Gulf of Mexico is worth watching
In the Gulf of Mexico, heavy thunderstorm activity has diminished since Monday along a weak cold front stretching from South Florida to the Louisiana coastal waters. Some models show a weak area of low pressure developing along this front and moving westwards over Texas by Friday, and we should keep an eye on this region for development.


Figure 2. MODIS true-color image of Hurricane Marie in the Eastern Pacific taken at approximately 18:15 UTC (2:15 pm EDT) on August 25, 2014. At the time, Marie was a Category 4 storm with 145 mph winds. Image credit: NASA.

Powerful Hurricane Marie generating huge waves in Eastern Pacific
The Eastern Pacific’s Hurricane Marie had weakened to a Category 2 storm with 105 mph winds on Tuesday morning, but was still generating huge swells that were bringing large waves to the coasts of Southern California and Mexico’s Baja Peninsula. At 5 am EDT on Tuesday, Marie’s tropical storm-force winds covered a huge area of ocean, up to 275 miles from the center, and 12-foot high seas extended up to 550 miles from the center. A High Surf Advisory is in effect for Los Angeles, where waves of 10 – 15 feet will potentially cause structural damage to piers and beachside property as well as significant beach erosion. The powerful surf will be accompanied by strong rip currents and long-shore currents, making for very hazardous swimming and surfing conditions through Thursday. Satellite loops on Tuesday morning showed a steady degradation of Marie’s cloud pattern, with the eyewall cloud tops warming and the areal coverage of the strongest thunderstorms decreasing. The storm is headed to the northwest over cooler waters and into drier air, and will not affect any land areas.

You can see a spectacular loop of infrared satellite images of Marie as it intensified into a Category 5 storm on Sunday at the CIMSS University of Wisconsin.

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2776