Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 6:12 AM GMT on July 30, 2013
A tropical wave, the remnants of Dorian, are located to the north of Hispaniola. Shower activity has increased again, but it remains disorganized; in addition, surface pressures are high, and there are no signs of a surface circulation.
Figure 1. Latest infrared satellite image of Invest 91L. Image credit: NOAA's Satellite Services Division (SSD).
The ongoing convective burst should not be taken as a sign that Dorian is trying to regenerate. There is still plenty of shear over the system, as evidenced by the rather flat outflow pattern along the west side; indeed, satellite analysis over the last several hours suggests that the upper tropospheric outflow associated with this system was actually better defined earlier, signifying another increase in shear.
Based on current and forecast trends, westerly shear is likely going to continue afflicting the system for the next 48 hours, and may actually increase a little during this time. Afterward, there is some indication that the upper flow may relax somewhat when the system reaches the Straits of Florida in three to four days, but considering the lack of a surface reflection up to this point, I question the system's ability to take advantage of this.
The wave appears to be moving westward again based on low-cloud lines from shortwave infrared satellite imagery; this could have been due to a lack of convection from a few hours ago. With the recent burst, the environmental steering favors a continued west-northwest track, north of the northern coast of Cuba, through the Florida Straits, and into the Gulf of Mexico thereafter. Since there is no well-defined center, the global models are of little practical value in this particular instance, so I relied instead upon the steering forecasts from the GFS and CMC for the next six days, which suggests the pattern over the Gulf favors the system moving into the northern or western Gulf Coast, a solution which has at times been supported by the statistical and dynamical model guidance.
The chance for redevelopment is quickly closing, and environmental conditions do not favor this system becoming a tropical cyclone again.
We may have to wait until the high weakens before we see any real development. Many active seasons in the Atlantic did not begin until the third or fourth week of August, including the volatile 1998 season, which saw Georges impact the northern Gulf Coast as a Category 2, and Mitch, which became a Category 5 and killed nearly 20,000 in Central America primarily due to floods. Things will get active, and the 500 mb pattern so far still shows no signs of budging, and favors a very active year for the United States.
Probability of development in 48 hours: 20%
Flossie has weakened to a tropical depression, but continues to lash the Hawaiian Islands with heavy rains and tropical storm force winds. As of the latest advisory from the Central Pacific Hurricane Center, the following information was available on the tropical cyclone:
Wind: 35 mph, with higher gusts
Location: 21.3N 156.5W
Movement: WNW at 18 mph
Pressure: 1002 mb
Possibly due to slightly warmer waters along the islands -- along with orographic lift from the rugged terrain on the islands, satellite and radar data suggest a rather vigorous burst of convection. This convection is located primarily to the south of the center in a convective band, the displacement due to moderate northerly to northwesterly shear caused by an upper-level high to the north. The global models think that this shear will continue, so there is no reason to assume any restrengthening of the storm in spite of the ongoing convection, which is actually dwindling as I write this.
Figure 2. Latest infrared satellite image of Tropical Depression Flossie. Image credit: NOAA's Satellite Services Division (SSD).
Satellite, radar, and microwave fixes indicate that Flossie continues to move toward the west-northwest, which would go well with the synoptic environmental steering. Virtually all of the guidance suggests that the storm will pass near over Kauai within the next 6 to 8 hours, and that is what I will forecast as well; however, in this particular instance, most of the associated weather does not accompany the center, so unless things change within the convective regime soon, Kauai and the remainder of the Hawaiian Islands will feel the primary effects as Flossie moves by to the north. A continued west-northwest motion is expected over the next several days, in agreement with the guidance, as Flossie approaches a break in the subtropical ridge.
The primary hazard with Flossie continues to be heavy rainfall. Doppler radar estimates have begun to show a developing swath of 2 to 4 inch rains over much of Maui County, perhaps not coincidentally after the new convective burst began around 0230 UTC. The National Weather Service office in Honolulu has issued flash flood watches for the entire archipelago, including a stray flash flood warning on the island of Maui in Maui County, incidentally where the doppler estimates showed the greatest estimated rainfall.
While the primary threat remains the potential for heavy rains and flash flooding, there have been some reports of tropical storm force wind gusts in the state, with an observing station in Kahului on Maui County recently reporting a sustained wind of 33 mph, with a gust to 46 mph in a strong rainband. These winds will likely continue as long as some semblance of convection remains; despite its weakened state, Flossie possesses a rather vigorous surface circulation, and it would not take a lot of thunderstorms to bring down strong winds aloft to the surface, especially in gusts. The wind threat will be maximized along communities in higher elevations, and will likely cause power outages and some minor tree damage.
High surf and coastal erosion will also be a significant concern.
Due to the limitations of the track map I typically use to draw tracks in this basin, I am unable to furnish a single forecast point for today, but I am in pretty good agreement with the CPHC's official track. Because of those limitations, I will not be posting an intensity forecast either, since they kind of go hand in hand.
CPHC storm information
WTPA31 PHFO 300404 CCA
TROPICAL DEPRESSION FLOSSIE ADVISORY NUMBER 21
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062013
500 PM HST MON JUL 29 2013
...FLOSSIE WEAKENS TO A TROPICAL DEPRESSION JUST NORTH OF MAUI...
SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
ABOUT 145 MI...230 KM NW OF HILO HAWAII
ABOUT 90 MI...145 KM E OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES
WATCHES AND WARNINGS
CHANGES WITH THIS ADVISORY...
ALL TROPICAL STORM WARNINGS HAVE BEEN DISCONTINUED.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
THERE ARE NO WATCHES OR WARNINGS IN EFFECT.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY THE NATIONAL WEATHER SERVICE FORECAST OFFICE IN
DISCUSSION AND 48-HOUR OUTLOOK
AT 500 PM HST...0300 UTC...THE CENTER OF TROPICAL DEPRESSION FLOSSIE
WAS LOCATED NEAR LATITUDE 21.3 NORTH...LONGITUDE 156.5 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30
MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. SOME WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB...29.59 INCHES.
HAZARDS AFFECTING LAND
WIND...TROPICAL STORM FORCE WIND GUSTS ARE POSSIBLE THIS EVENING AND
OVERNIGHT. LOCALLY GUSTY WINDS WILL LIKELY CONTINUE ON TUESDAY OVER
THE CENTRAL AND WESTERN ISLANDS.
RAINFALL...LOCALLY HEAVY RAINFALL IS PRESENTLY OCCURRING OVER
PORTIONS OF THE BIG ISLAND. LOCALLY HEAVY RAINFALL IS EXPECTED THIS
EVENING AND OVERNIGHT OVER MAUI COUNTY...SPREADING TO OAHU AND
KAUAI LATER TONIGHT. FLOSSIE IS EXPECTED TO PRODUCE TOTAL RAINFALL
AMOUNTS OF 2 TO 4 INCHES OVER THE BIG ISLAND WITH ISOLATED AMOUNTS
UP TO 6 INCHES. OVER THE REST OF THE STATE TOTAL RAINFALL AMOUNTS
WILL BE 1 TO 2 INCHES WITH ISOLATED AMOUNTS UP TO 6 INCHES. THIS
RAINFALL COULD CAUSE LIFE-THREATENING FLASH FLOODS AND MUD
SLIDES...ESPECIALLY IN THE MOUNTAINS.
SURF...DANGEROUS HIGH SURF WILL CONTINUE TO AFFECT EAST FACING
SHORES. THE SURF WILL BEGIN TO SUBSIDE TONIGHT ALONG EAST FACING
SHORES OF THE BIG ISLAND. LARGE SURF WILL CONTINUE ON TUESDAY FOR
THE REST OF THE STATE BEFORE SUBSIDING TUESDAY NIGHT. THE LARGE
SURF MAY CAUSE COASTAL ROAD CLOSURES.
NEXT ADVISORY...1100 PM HST.
An area of low pressure located about 850 miles south-southwest of the southern tip of Baja California is showing signs of organization. Evening satellite images show a banding-type cloud pattern, which is normally a sign of a developing system.
Figure 3. Latest infrared satellite image of Invest 99E. Image credit: NOAA's Satellite Services Division (SSD).
Upper-level winds are forecast to become more conducive for development over the next couple of days, particularly beyond 24 hours when the GFS builds an upper-level anticyclone over the disturbance. There is a developing upper low off the Pacific northwest, which the models show digging southeastward over the next 48 hours; this is expected to cause a general west-northwestward motion during the next two to three days, with the possibility of a more westward-moving system thereafter as the trough lifts north and the subtropical ridge rebuilds to the north of the system. Long-range predictions suggest this system will enter the central Pacific basin over a week from now, but its potential threat to Hawaii remains uncertain.
Probability of development in 48 hours: 30%
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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