Tropical weather analysis - July 3, 2014

By: KoritheMan , 6:56 AM GMT on July 03, 2014

Notice: All information contained herein is purely a product of my own interpretation of the available data. It is not intended to supersede or replace the directive or forecasts of the National Hurricane Center. Regardless of how well I can identify a trough and a ridge on water vapor imagery, the ultimate go to source should always be the National Weather Service and its affiliates.

Arthur

Arthur remains just under hurricane strength as of the latest NHC advisory package:

Wind: 70 mph, with higher gusts
Location: 30.9°N 79.1°W
Movement: N at 8 mph
Pressure: 988 mb

Satellite images have shown periodic hints of an eye, which recent microwave and radar data confirms is fairly strong aloft. Satellite estimates from TAFB and UW-CIMSS ADT support hurricane strength, but this has been the case since about 0z. Pending investigation from an en route aircraft, they decided to conservatively hold the intensity at 60 kt given some discrepancies in the observed flight-level and SFMR winds. However, with the central pressure already down to 988 mb and likely to continue to slowly fall, it is likely we will have a hurricane sometime this morning. Upper-tropospheric outflow is not particularly well-defined to the west, but that appears to be more a direct symptom of continued dry air than a large-scale increase in shear.



Figure 1. Latest infrared satellite image of Tropical Storm Arthur. Image credit: NOAA's Satellite Services Division (SSD).

Arthur is once again presenting a difficult intensity forecast challenge. On one hand, the cyclone appears to have a solid inner core now, as evidenced by the occasional appearance of an eye in infrared satellite data. On the other hand, evening upper air data from Jacksonville and Charleston still show a fairly pronounced pocket of dry air in the middle troposphere, and there has been some hints on long-range doppler radar that the eye has been unable to close off, remaining largely open on the southwestern side. The center has been easy to follow on both the long-range Jacksonville and Charleston radar. The former is closer to the center of Arthur, suggesting that it has a better sample on the low-levels of the storm. The data from that site indicates that precipitation is attempting to consolidate around the relatively vacuous southwestern side. Should this trend continue, Arthur would be able to intensify. Small circulations generally fare better with warding off dry air entrainment than do comparatively larger ones, and although Arthur is likely to grow as it accelerates northeastward, any possible dry air intrusions should not be enough to eliminate at least gradual intensification. My forecast is largely the same one as the I published yesterday, and shows Arthur becoming a hurricane soon, followed by a peak of 75 kt as the cyclone approaches the Outer Banks. It should be noted that several coastal and offshore buoys indicate that ocean temperatures along the path of Arthur are about .5C warmer than the SHIPS integration thinks they are, even all the way up to the Outer Banks. If the cyclone can thwart the dry air from its core, there is a remote possibility of Arthur attaining Category 2 status. Arthur is forecast to weaken rather quickly after passing the Outer Banks as shear and cold waters induce baroclinicity and cause extratropical transition. Although no forecast point is provided out to 120 hours, it's merely due to a limitation of the map I use to create the track forecasts; Arthur is likely to linger around for at least a day longer than indicated below.

Arthur has stubbornly refused to make the anticipated poleward turn this evening, as several radar and satellite fixes show. Indeed, the National Hurricane Center just released the 6z intermediate advisory, and shows a due north (360°) motion during the past three hours. Having said that, water vapor imagery shows that the mid- to upper-level trough expected to recurve the cyclone is progressively amplifying southward, and as a result the tropical storm is likely to begin turning very soon. My forecast track continues to be along the western edge of the model consensus, if not a shade to the west. It should be noted that if Arthur continues moving northward and delays the onset of recurvature, there could be significant implications for the North Carolina coast. While I cannot rule out a possible landfall on the mainland, the odds of this happening appear low at this time. Interests in the hurricane warning area should closely monitor the progress of Arthur. Sustained hurricane-force winds could still affect the Outer Banks in Arthur's northern eyewall, during which time the cyclone is expected to be an intensifying hurricane. The National Hurricane Center wind speed probability product indicates a 30% chance that Cape Hatteras will experience sustained hurricane-force winds as Arthur makes its closest approach to the Outer Banks between late Thursday night and Friday morning.

Heavy rainfall is possible north of the storm track once Arthur interacts more fully with the approaching frontal system. Most of this rain is likely to fall along immediate coastal areas of North Carolina, but it is not out of the question they could affect portions of the South Carolina coast. The tornado risk appears minimal, as Arthur's right-front quadrant will likely remain offshore.

The latest NHC storm surge inundation map shows that a storm on Arthur's track and intensity could produce a storm surge of up to 3 feet along the Outer Banks and immediate coastal areas of the state.

After passing the Outer Banks, Arthur is forecast to accelerate further until the end of the forecast period, when the guidance suggests it could slow as it orbits around a larger extratropical cyclone over the north Atlantic.

A tropical storm warning remains in effect from South Santee River, South Carolina to south of Surf City. Tropical storm force sustained winds will probably stay offshore if Arthur follows the current track, but interests in the warning area should monitor any significant westward deviations from Arthur.

Intensity forecast

Initial 07/03 0300Z 30.6°N 79.1°W 60 kt 70 mph
12 hour 07/03 1200Z 31.7°N 78.7°W 65 kt 75 mph
24 hour 07/04 0000Z 33.3°N 77.3°W 75 kt 85 mph
36 hour 07/04 1200Z 35.4°N 75.1°W 75 kt 85 mph
48 hour 07/05 0000Z 38.6°N 71.1°W 70 kt 80 mph
72 hour 07/06 0000Z 44.9°N 63.1°W 60 kt 70 mph: extratropical
96 hour 07/07 0000Z 50.6°N 54.7°W 45 kt 50 mph: extratropical

Track forecast



Figure 2. My forecast track for Arthur. The track was made using the 3z coordinates, but for all intents and purposes this will not make a large difference.

NHC storm information

000
WTNT31 KNHC 030549
TCPAT1

BULLETIN
TROPICAL STORM ARTHUR INTERMEDIATE ADVISORY NUMBER 9A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012014
200 AM EDT THU JUL 03 2014

...ARTHUR NEAR HURRICANE STRENGTH...
...AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INVESTIGATING...


SUMMARY OF 200 AM EDT...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...30.9N 79.1W
ABOUT 365 MI...585 KM SW OF CAPE HATTERAS NORTH CAROLINA
ABOUT 140 MI...230 KM SSE OF CHARLESTON SOUTH CAROLINA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...N OR 360 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...988 MB...29.18 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* SURF CITY NORTHWARD TO DUCK
* PAMLICO SOUND
* EASTERN ALBEMARLE SOUND

A HURRICANE WATCH IS IN EFFECT FOR...
* LITTLE RIVER INLET TO SOUTH OF SURF CITY

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* SOUTH SANTEE RIVER SOUTH CAROLINA TO SOUTH OF SURF CITY
* NORTH OF DUCK TO CAPE CHARLES LIGHT VIRGINIA...NOT INCLUDING
CHEASEPEAKE BAY
* WESTERN ALBEMARLE SOUND

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE
AND PROPERTY SHOULD BE RUSHED TO COMPLETION.

A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE
WITHIN THE WATCH AREA...IN THIS CASE WITHIN THE NEXT 24 HOURS. ANY
DEVIATION OF THE FORECAST TRACK TO THE LEFT...OR AN INCREASE IN THE
FORECAST SIZE OF ARTHUR WOULD LIKELY REQUIRE THE ISSUANCE OF
HURRICANE WARNINGS FOR ALL OR PART OF THE HURRICANE WATCH AREA.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA.

INTERESTS ALONG THE UNITED STATES EAST COAST NORTH OF THE WARNING
AREA...PRIMARILY IN SOUTHEASTERN NEW ENGLAND...SHOULD MONITOR THE
PROGRESS OF ARTHUR.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR
LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM EDT...0600 UTC...THE CENTER OF TROPICAL STORM ARTHUR WAS
LOCATED BY NOAA DOPPLER RADARS NEAR LATITUDE 30.9 NORTH...LONGITUDE
79.1 WEST. ARTHUR IS MOVING TOWARD THE NORTH NEAR 8 MPH...13 KM/H. A
TURN TOWARD THE NORTH-NORTHEAST IS EXPECTED TODAY...FOLLOWED BY A
TURN TOWARD THE NORTHEAST WITH AN INCREASE IN FORWARD SPEED TONIGHT.
ON THE FORECAST TRACK...THE CORE OF ARTHUR IS EXPECTED TO APPROACH
THE COAST IN THE HURRICANE WARNING AREA TONIGHT.

MAXIMUM SUSTAINED WINDS ARE NEAR 70 MPH...110 KM/H...WITH HIGHER
GUSTS. STRENGTHENING IS FORECAST...AND ARTHUR IS EXPECTED TO BECOME
A HURRICANE SOON. AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT
WILL BE INVESTIGATING ARTHUR THIS MORNING.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 90 MILES...150 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 988 MB...29.18 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE TROPICAL
STORM WATCH AREA BY THIS AFTERNOON...AND ARE EXPECTED TO SPREAD
NORTHWARD WITHIN THE TROPICAL STORM WARNING AND HURRICANE WARNING
AREAS LATER TODAY AND TONIGHT. HURRICANE CONDITIONS ARE EXPECTED
WITHIN THE HURRICANE WARNING AREA BY TONIGHT.

STORM SURGE...THE COMBINATION OF A DANGEROUS STORM SURGE AND THE
TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY
RISING WATERS. THE WATER COULD REACH THE FOLLOWING HEIGHTS ABOVE
GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

NORTH CAROLINA OUTER BANKS...2 TO 4 FT
PAMLICO AND ALBEMARLE SOUNDS...2 TO 4 FT
SOUTHERN NORTH CAROLINA AND NORTHEASTERN SOUTH CAROLINA...1 TO 3 FT
EXTREME SOUTHEASTERN VIRGINIA...1 TO 2 FT

THE HIGHEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST IN AREAS OF
ONSHORE FLOW. THE SURGE WILL BE ACCOMPANIED BY LARGE AND DAMAGING
WAVES. SURGE-RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE
SURGE AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT
DISTANCES. FOR INFORMATION SPECIFIC TO YOUR AREA...PLEASE SEE
PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE AND
THE NEW EXPERIMENTAL POTENTIAL STORM SURGE FLOODING MAP FOR MORE
DETAILS.

RAINFALL...RAINFALL ACCUMULATIONS OF 2 TO 4 INCHES...WITH ISOLATED
MAXIMUM AMOUNTS OF 6 INCHES...ARE EXPECTED OVER COASTAL AREAS OF
NORTH CAROLINA THROUGH FRIDAY. RAINFALL AMOUNTS NEAR AN INCH ARE
POSSIBLE ON THE EAST COAST OF FLORIDA.

SURF...SWELLS GENERATED BY ARTHUR ARE AFFECTING AREAS FROM THE
EAST-CENTRAL COAST OF FLORIDA NORTHWARD TO SOUTH CAROLINA. THESE
SWELLS ARE EXPECTED TO CAUSE LIFE-THREATENING SURF AND RIP CURRENTS.
FOR MORE INFORMATION...PLEASE MONITOR PRODUCTS ISSUED BY YOUR LOCAL
NATIONAL WEATHER SERVICE FORECAST OFFICE.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM EDT.

$$
FORECASTER BRENNAN/STEWART


Douglas

Tenacious Douglas holds on as a tropical storm. As of the 3Z NHC advisory, the following information was available on Douglas:

Wind: 40 mph, with higher gusts
Location: 20.2°N 116.3°W
Movement: NNW at 2 mph
Pressure: 1004 mb

Douglas is still producing some fairly deep convection for a mid-latitude system over sub-26C waters, but as soon as the tropical storm begins to accelerate, it will not be long for this world. Earlier scatterometer data suggest that Douglas continues to possess an unusually large wind field.



Figure 3. Latest infrared satellite image of Tropical Storm Douglas. Image credit: NOAA's Satellite Services Division (SSD).

The cyclone remains embedded in an environment of weak vertical shear, and this is likely to continue for several more days, so even though Douglas will be moving across progressively cooler water after it accelerates, only a gradual spin down is expected of this rather large circulation. There isn't much new to say on Douglas except that the GFS now shows the system losing its identity in the trade wind belt in less than 120 hours. Given that this seems reasonable, I have chosen to terminate a 120 hour forecast position from this forecast package. The ECMWF remains a little stronger, so it's not completely out of the question that Douglas or its remnants could persist a little longer.

Douglas continues to meander very slowly north-northwestward, and doesn't appear to have gained much... if any... forward momentum over the last few hours. Water vapor and UW-CIMSS analyses indicate that Douglas is embedded in a region of very weak steering as broad downstream troughing continues to push against the subtropical ridge. The model guidance indicates a restrengthening of the ridge to the north of Douglas over the next couple of days, which is expected to result in a gradual acceleration to the west-northwest and then west if it persists beyond day four. My forecast track is similar to the current National Hurricane Center prediction except noticeably east at longer ranges because I terminate the track after day four.

Intensity forecast

Initial 07/03 0300Z 20.2°N 116.3°W 35 kt 40 mph
12 hour 07/03 1200Z 20.4°N 116.5°W 35 kt 40 mph
24 hour 07/04 0000Z 20.6°N 116.9°W 30 kt 35 mph
36 hour 07/04 1200Z 20.9°N 117.7°W 30 kt 35 mph: post-tropical/remnant low
48 hour 07/05 0000Z 21.5°N 119.2°W 25 kt 30 mph: post-tropical/remnant low
72 hour 07/06 0000Z 22.7°N 121.6°W 20 kt 25 mph: post-tropical/remnant low
96 hour 07/07 0000Z 24.1°N 125.1°W 20 kt 25 mph: post-tropical/remnant low
120 hour 07/08: dissipated

Track forecast



Figure 4. My forecast track for Douglas.


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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3. WunderAlertBot (Admin)
7:34 AM GMT on July 04, 2014
KoritheMan has created a new entry.
2. Dragod66
11:11 AM GMT on July 03, 2014
No mention on impacts to Canada eh? ;)
Member Since: December 31, 1969 Posts: Comments:
1. Wolfberry
7:29 AM GMT on July 03, 2014
Thanks Kori, informative and great to read..
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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