Hurricane season passing its prime

Thunderstorm studies continue

Sept. 15, 1998: (this is the 16th in a series of stories covering the ongoing CAMEX mission to hunt hurricane data in a way not done since the 50s. Other stories are linked in below.)

The 1998 hurricane season is passing its prime with new hurricane candidates forming for the CAMEX-3 team to study. Meanwhile, the CAMEX team plans a set of flights with the DC-8, ER-2, and Citation aircraft to take measurements in support of the Tropical Rainfall Measuring Mission (TRMM).

Right: A rainbow brushes the propeller tips on an Air Force WC-130 Hurricane Hunter. This picture was taken as the crew returned from a day of patrolling Hurricane Frances which, by Monday morning, had worn itself down to a tropical depression (see GOES image, below left) soaking the coast of Texas. (Click here for information of the Hurricane Hunters)

On Monday, the DC-8 and Citation flew through convective weather cells off Cape Canaveral while the ER-2 stayed at Patrick AFB, Fla., because of strong crosswinds.

"Climatologically, we are nearing the end of the Cape Verde (Africa) season," wrote meteorologist Ed Bensman in today's forecast. The Atlantic Ocean off Cape Verde is where a large number of hurricanes are spawned in the late summer (in addition to those that form over the Gulf of Mexico). They then pick up energy as they range westward and then slam into the American southeast.

But not for the past few days.

In the tropics, the 1008mb low northwest of the Cape Verde Islands moved to the north and dissipated. To the south of the islands a new, better-organized low emerged off the coast of Africa overnight. Satellite animation of this feature clearly shows low-level organization and rotation. The system is currently near 10 deg. N, 20 deg. W and is moving toward the west. This is the most impressive wave in the last few weeks to emerge from west Africa.

Left: An infrared image from GOES-8 Monday shows rainstorms, but no large, organized activity.

Closer to the U.S., a system continues to feed convection from the Gulf of Mexico northward into the remnants of Hurricane Frances. In the western Caribbean moderate to strong convection continues in this region, but still with little sign of organization. However, most models continue to develop a system in this region with motion toward the Yucatan Channel and then into the central Gulf of Mexico.

Over the next 1 to 2 days, the National Hurricane Center will monitor the area of convection off the west coast of Africa. This system should continue to move to the west and may undercut the trough in the central Atlantic. If it does not, it will be sheared by this trough and will likely recurve in the central Atlantic. If this system does move under the trough, it will likely make it to the Lesser Antilles by the end of the forecast period.

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For the next 2 to 3 days, forecast models for the tropics begin to develop a broad area of low pressure in the central Gulf of Mexico. With pressures lowered by Earl and Frances, the pressure gradient across Florida will increase as the strong surface high moves down the east coast. Forecasts for the Gulf low vary. Several easterly waves across the southern Caribbean are forecast to continue westward, but none is forecast to develop into significant tropical systems through this period. The wave off Africa today is forecast during this period to diminish across the central Atlantic.

Finally, over the next 3 to 5 days, a low off Africa - if it survives the trough in the central Atlantic - will be nearing the Lesser Antilles islands. Given the latitude (10N) that this system emerged from the coast at, it is likely that this low would move across the Caribbean Sea south of the northern Lesser and Greater Antilles. At such long lead times it is impossible to say the exact track of this low.

Meanwhile, the CAMEX-3 team is staying busy working as the TEFLUN team - Texas and Florida Underflights - supporting validation of the instruments on TRMM.

Note: More details are available in the NASA press release describing CAMEX-3. Check back as hurricane season progresses. We will post science updates as the campaign develops. PIX: High resolution scans of 35mm camera photos from the CAMEX-3 campaign are available from Public Affairs Office at NASA headquarters. Please call the NASA Headquarters Photo Department at 202-358-1900, or contact Bill Ingalls at bingalls@hq.nasa.gov. CAMEX Series Headlines August 12: Overview CAMEX story , describes the program in detail. August 13: CAMEX maiden flight , for calibration of TRMM satellite instruments August 14: CAMEX test flights , CAMEX flies over tropical storm weather in successful calibration run August 18: CAMEX aircraft make second flight with TRMM , second calibration run for TRMM August 20: CAMEX may get first chance at a tropical storm , later this week  August 21: Here comes Bonnie! , CAMEX scheduled to fly over T.S. Bonnie  August 22: West by Northwest , CAMEX team may have to evacuate to Georgia  August 24: Eye-to-eye, and Bonnie winks, CAMEX team makes first flight through eye  August 25: Snow in August, Bonnie surprises the hurricane team  August 26: Camera of many colors Hurricane hunters using advanced scanner to peer into storms   August 28: Preparing for Danielle NASA team takes break as Bonnie fades away August 31: Quite a Windfall Hurricane team completes first half of unique science campaign. Includes listing of August flights and aircraft and spacecraft used in CAMEX-3. September 2: Bonnie Cuts a Towering Figure Satellite radar shows mountainous cloud chimney September 4: Hurricane team studies Earl Four aircraft probe storm September 10: NASA team awaits next hurricane September 16: Hurricane season passing its prime Thunderstorm studies continue as a new hurricane candidate wends its way from Africa. (this story) September 18: Two new storms brewing for hurricane research team Scientists fly 4 out of 5 days, clear air sampled over the Bahamas, oceanic convection data collected east of Cape Canaveral September 21:The last hurricane - CAMEX team wrapping up campaign with flights into Georges September 23: Hurricane Georges puts on a light show - CAMEX team treated to purple sprites and weird lightning NCAR has an extensive writeup on the GPS dropsondes used in CAMEX-3 and other atmospheric campaigns. A new study - not related to CAMEX-3 - by the Arizona State University suggests a link between hurricanes in the northwest Atlantic and air pollution.

CAMEX-3 - the third Convection and Moisture Experiment - is an interagency project to measure hurricane dynamics at high altitude, a method never employed before over Atlantic storms. From this, scientists hope to understand better how hurricanes are powered and to improve the tools they use to predict hurricane intensity.

An overview story (Aug. 12, 1998) describes the program in detail. The study is part of NASA's Earth Science enterprise to better understand the total Earth system and the effects of natural and human-induced changes on the global environment. A midterm story (Aug. 31, 1998) reviews the first month of operations and the windfall of data.

Measuring distance and speed

Because meteorology and aeronautics first used modified nautical charts, their data bases are in nautical miles and knots (nautical miles per hour). In these stories, we use Standard International ("metric") units first, and give more familiar measurements in English units and the original measurements in nautical units. Because of rounding and because the wind speeds originally are expressed in knots, km/h speeds to knots may be slightly different from the numbers in the story.

Standard International Units: 

km - kilometer (1 km = 0.62 smi = 0.54 nmi) 

km/h - kilometers per hour 

English (or US) units: 

mi, or smi - miles (statute miles; 1 smi = 0.87 nmi = 1.61 km)
mph - (statute) miles per hour 

Nautical units: 

nmi - nautical miles (1 nmi = 1.15 smi= 1.85 km) 

kts - knots (nautical miles per hour) 

 

Web Links

CAMEX-3 home page contains links to daily flight operations and instrument descriptions. Lightning Imaging Sensor aboard the TRMM satellite observes lightning from above the clouds - and my lead to better warnings on the ground. MACAWS uses the Doppler effect (red and blue shifts) to measure wind velocity. SPARCLE is a Space Shuttle experiment set for 2001 to demonstrate laser wind measurement from space.