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E Pacific Tropical Action of 2014

Yellow Evan

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icebreaker5221

icebreaker5221

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A G-IV mission is tasked for tomorrow and a low level flight for Wednesday the 6th with yesterdays issuance of TCPOD. It is also noteworthy that the GFS and Euro are suggesting a close brush with Hawaii of two tropical cyclones in fairly short order which would be a bit unusual for the Island chain.

 

Not just a bit unusual, but completely unprecedented.  1982 came close, with a TD Daniel in late July and TS Gilma a week later (and then hurricane Iwa later that same season).  However, both Daniel and Gilma were rapidly deteriorating as they approached the big island, and I'm not sure I would classify either as legitimate threats.

 

1992 also sorta featured a 1-2 punch with Hurricane Iniki and TD Orlene, although Orlene was nothing but a rain maker as it dissipated over the big island.

 

 

Nice annular structure!  That should help Iselle to maintain a stronger intensity than it otherwise would in decreasing SSTs, as annular cyclones tend to thrive in 26-27 C SSTs.  How well it survives an increasingly dry environment remains to be seen, although some weakening over the next few days is a virtual lock. 

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Srain

Srain

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After doing some research and chatting with my friend wxman57, we found that the Hawaiian Island Chain has never received a direct hit from a Hurricane from the E/ESE. The only known dying TC to hit  from the E was a Not Named storm on August 8, 1958 that was a rapidly weakening TD that made landfall near Hilo. The only known direct Hurricane strikes to Hawaii have come from the S and SSE Iniki/1992 CAT 4 and Dot/1959 CAT 1, which struck the Island of Kauai. Iwa 1982 passed just NW of Kauai, but missed. There have been Tropical Storms pass N and S of the Island chain.

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IsentropicLift

IsentropicLift

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My understanding was that, all else being equal, annular hurricanes weaken more slowly than other storms.  Is this true and is there a chance of a more substantial impact to Hawaii because this storm has made this transition?

True annular hurricanes don't undergo eyewall replacement cycles. That's what allows them to maintain intensity for longer periods. They also tend to weaken very slowly after reaching peak intensity.

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phil882

phil882

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True annular hurricanes don't undergo eyewall replacement cycles. That's what allows them to maintain intensity for longer periods. They also tend to weaken very slowly after reaching peak intensity.

 

That's not entirely true... as Isabel (2003) underwent multiple EWRC in between its period of annular characteristics.

 

Its still not fully understood why annular hurricanes weaken slower than a traditional TC, but it possibly has something to do with the distribution of diabatic heating across the TC. When you don't have any principle or secondary rainbains, the diabatic heating gradient across the TC is more uniform and stronger between the very high diabatic heating in the eyewall, and the relatively low diabatic heating outside of the TC core.

 

This is what drives the wind field of the TC, and its also a likely process that results in the development of secondary eyewalls, when diabatic heating starts to become focused in a rainband ring around the original eyewall. However, this also weakens the wind field and allows for dry air to be advected in between the rainbands as the diabatic heating gradient broadens. The end result is a broader wind field with a lower wind maxima. The WPAC TCs are a great example of this happening the environment is always moist and warm around the TC and convection can fire everywhere well outside of the main TC core. Its why sometimes monsoon depressions can't develop a nice inner core (see Nakari) because the diabatic heating gradient that drives the wind field is simply too broad with competing convection all around the circulation of the monsoon depression.

 

Annular TCs don't undergo EWRC the same way as regular TCs do. One thing that is just as important as the fact that these TCs don't have any rainbands is how thick the eyewall convection is. Annular TCs often have an extra thick eyewall, and when they undergo an EWRC, its simply replacing the radius of that inner most ring of convection. That's how Isabel became larger and larger with time, the inner eyewall convection faded, but was simply replaced with the still very deep and vigorous convection just outside of that radius. The circular band of convection did not develop any breaks and dry air could not get into the inner core. The diabatic heating gradient also wasn't smoothed out because all of the convection remained in the inner core. Since there were lower SSTs and drier air surrounding the system, rainbands couldn't develop outside of the inner core, and the tight structure of the TC was preserved. 

 

Now eventually a TC can become large enough that this diabatic heating gradient is no longer sustainable and breaks do start to appear in the inner core convection (e.g. Isabel 2003, Jerelawat 2000) or it can also move into an environment with stronger vertical wind shear that creates asymmetries in the storm structure that allows dry air to break up this ring of convection. That's why annular hurricanes are rare, you need the combination of very low vertical wind shear, and also a relatively dry and stable environment AFTER the TC has become self sustaining and has developed a formidable PV tower. You don't see weaker TCs turn into annular hurricanes because you already need a well developed inner core that moves into this more stable environment. The initial environment with Iselle was moist and it moves into this more stable environment after it had developed a organized inner core. 

 

3TkFhd3.jpg

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Srain

Srain

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An interesting and potentially historic week ahead, tropically speaking for Hawaii. The last 12 suite of operational Global guidance suggest a rather strong TS Iselle will make its approach late Thursday into Friday from an Easterly direction. While the intensity remains very uncertain, there is warmer water E of Hawaii that may keep Iselle a bit stronger and possibly allow for a steady state as it approaches.

 

The global guidance is suggesting Julio may fair a bit better and provide for a stronger cyclone as it approaches Hawaii on Sunday from a ESE direction, slightly S of the Iselle expected track and receive the benefit of enhanced moisture throughout the column in the wake of Iselle. The intensity guidance is split between a stronger 100 kt cyclone to a near 70 kt cyclone. The NHS is taking a reasonable conservative approach and with additional data arriving particularly from the G-IV tasked missions this week, we should see some changes in what may well be two cyclones passing very near or over the Hawaiian Islands with a matter of 3-4 days later this week into the upcoming weekend.



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tmagan

tmagan

Posted
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Fairly bold wind forecast from NWSFO Honolulu:

HIZ025-051315-
BIG ISLAND NORTH AND EAST-
INCLUDING...HILO...VOLCANO...HONOKAA...KAMUELA
1215 PM HST MON AUG 4 2014
 
.THIS AFTERNOON...SUNNY WITH ISOLATED SHOWERS. HIGHS AROUND 85 AT
THE SHORE TO AROUND 72 AT 4000 FEET. EAST WINDS 10 TO 15 MPH.
CHANCE OF RAIN 20 PERCENT. 
.TONIGHT...MOSTLY CLOUDY WITH SCATTERED SHOWERS. LOWS AROUND
72 AT THE SHORE TO AROUND 55 AT 4000 FEET. NORTH WINDS 10 TO
15 MPH AND GUSTY. CHANCE OF RAIN 40 PERCENT. 
.TUESDAY...MOSTLY SUNNY. SCATTERED SHOWERS IN THE MORNING...THEN
ISOLATED SHOWERS IN THE AFTERNOON. HIGHS AROUND 85 AT THE SHORE
TO AROUND 72 AT 4000 FEET. NORTH WINDS 10 TO 15 MPH SHIFTING TO
THE NORTHEAST IN THE LATE MORNING AND AFTERNOON. GUSTS UP TO
30 MPH. CHANCE OF RAIN 40 PERCENT. 
.TUESDAY NIGHT...PARTLY CLOUDY IN THE EVENING THEN BECOMING
MOSTLY CLOUDY. SCATTERED SHOWERS. LOWS 53 TO 76. NORTH WINDS
10 TO 15 MPH. CHANCE OF RAIN 40 PERCENT. 
.WEDNESDAY...MOSTLY SUNNY. SCATTERED SHOWERS IN THE MORNING...
THEN ISOLATED SHOWERS IN THE AFTERNOON. HIGHS 65 TO 85. NORTHEAST
WINDS 10 TO 15 MPH. CHANCE OF RAIN 40 PERCENT. 
.WEDNESDAY NIGHT...TROPICAL STORM CONDITIONS POSSIBLE. MOSTLY
CLOUDY. SCATTERED SHOWERS IN THE EVENING...THEN NUMEROUS SHOWERS
AFTER MIDNIGHT. LOWS 53 TO 76. NORTHEAST WINDS 10 TO 15 MPH.
CHANCE OF RAIN 70 PERCENT. 
.THURSDAY...TROPICAL STORM CONDITIONS POSSIBLE. FREQUENT SHOWERS.
LOCALLY HEAVY RAINFALL POSSIBLE. HIGHS 63 TO 82. NORTHEAST WINDS
15 TO 20 MPH WITH HIGHER GUSTS BECOMING NORTHWEST AND INCREASING
TO 50 TO 60 MPH WITH GUSTS TO 90 MPH IN THE AFTERNOON. CHANCE OF
RAIN NEAR 100 PERCENT. 
.THURSDAY NIGHT...TROPICAL STORM CONDITIONS POSSIBLE. FREQUENT
SHOWERS. LOCALLY HEAVY RAINFALL POSSIBLE. LOWS 53 TO 76. SOUTH
WINDS 50 TO 60 MPH WITH GUSTS TO 90 MPH BECOMING EAST AND
DECREASING TO 15 TO 20 MPH AND GUSTY AFTER MIDNIGHT. CHANCE OF
RAIN NEAR 100 PERCENT. 
.FRIDAY...CLOUDY. FREQUENT SHOWERS IN THE MORNING...THEN NUMEROUS
SHOWERS IN THE AFTERNOON. LOCALLY HEAVY RAINFALL POSSIBLE. HIGHS
60 TO 78. NORTHEAST WINDS 10 TO 15 MPH. CHANCE OF RAIN
80 PERCENT. 
.FRIDAY NIGHT...MOSTLY CLOUDY WITH NUMEROUS SHOWERS. LOCALLY
HEAVY RAINFALL POSSIBLE. LOWS 53 TO 76. NORTHEAST WINDS 10 TO
15 MPH. CHANCE OF RAIN 70 PERCENT. 
.SATURDAY...CLOUDY WITH FREQUENT SHOWERS. LOCALLY HEAVY RAINFALL
POSSIBLE. HIGHS 64 TO 82. NORTHEAST WINDS 15 TO 20 MPH. CHANCE OF
RAIN 80 PERCENT. 
.SATURDAY NIGHT...CLOUDY WITH FREQUENT SHOWERS. LOCALLY HEAVY
RAINFALL POSSIBLE. LOWS 53 TO 76. NORTHEAST WINDS 15 TO 20 MPH.
CHANCE OF RAIN 80 PERCENT. 
.SUNDAY...CLOUDY WITH FREQUENT SHOWERS. LOCALLY HEAVY RAINFALL
POSSIBLE. HIGHS 64 TO 82. EAST WINDS 15 TO 20 MPH WITH HIGHER
GUSTS. CHANCE OF RAIN 80 PERCENT. 
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Yellow Evan

Yellow Evan

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After doing some research and chatting with my friend wxman57, we found that the Hawaiian Island Chain has never received a direct hit from a Hurricane from the E/ESE. The only known dying TC to hit  from the E was a Not Named storm on August 8, 1958 that was a rapidly weakening TD that made landfall near Hilo. The only known direct Hurricane strikes to Hawaii have come from the S and SSE Iniki/1992 CAT 4 and Dot/1959 CAT 1, which struck the Island of Kauai. Iwa 1982 passed just NW of Kauai, but missed. There have been Tropical Storms pass N and S of the Island chain.

 

Raymond 83, Eugene 92, Orlene 92, and Douglas 84 all came onshore as a TD.

 

Several other storms like Gil 83 and Hiki have passed through the island chain as a TS.

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Yellow Evan

Yellow Evan

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Looks like Iselle is improving this morning after a somewhat ragged appearance overnight. Cloud tops are cooling once again and outflow is improving. Latest Dvorak estimates have ticked up.

 

rb_lalo-animated.gif

 

Could this go back up to Cat 4 status? ATCF kept it at 110 knts.

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Srain

Srain

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MIMIC suggests Hurricane Iselle weakened slightly over night, but the inner core has completely wrapped around the center of circulation again and remains a very strong small intense cyclone that should reduce the chances of dry air intrusion into the inner core. The track has shift slightly S with the overnight guidance suggesting a potential strike to the Big Island of Hawaii may be likely during Thursday into Friday. The Central Pacific Hurricane Center will take over responsibility of forecasting and issuing advisories at 18Z today.

 

 

 

http://www.prh.noaa.gov/hnl/cphc/

 

TS Julio is moving rapidly to the W and Northeasterly shear has inhibited convection from wrapping around the Eastern semicircle of the cyclone. The shear is expect to decrease later today into tomorrow and allow for Julio to strengthen as the Ridge to the N builds allowing for a western motion to continue. The latest guidance is suggesting an approaching trough after Iselle passes Hawaii will pull Julio a bit to the NW prior to making its final approach to the Hawaiian Island this weekend. The intensity guidance continues to advertise Julio will achieve Hurricane status E of Hawaii and maintain Hurricane intensity as it passes just NW of the Island Chain. Expect additional changes in both track and intensity as the G-IV missions currently tasked provide additional information which should greatly improve the guidance data over the next couple of days.

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IsentropicLift

IsentropicLift

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Iselle is really starting to worry me. It really has 24-36 hours left to weaken, and at this rate, this could easily be a hurricane at landfall. Buildings in Hawaii aren't the best, and Hilo is very prone to storm surge.

My cousin is there this week on her honeymoon. Talk about terrible timing.
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icebreaker5221

icebreaker5221

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While all the focus is currently on Iselle and Julio, (and justifiably so), Hurricane Genevieve is still out there looking her best yet!  CPHC says major hurricane by 8pm HST tomorrow (Thu), but I'm thinking she's on the verge of that already.  She's also covered an impressive amount of longitude so far (invest 7/19, TD 7/25, remnant low 7/27, TD again 8/02).

 

post-378-0-95020000-1407366118_thumb.gif

 

post-378-0-96497100-1407366125_thumb.png

 

post-378-0-51402300-1407366137_thumb.gif

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wxtrackercody

wxtrackercody

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If I am reading the latest SHIPS guidance regarding Genevieve correctly, it represents a best fit to an annular structure.

You're not reading it wrong, but the analysis itself seems off. Genevieve is not an annular hurricane; it has too small of an eye and a prominent spiral band to the northwest.

 

The storm has exploded in intensity over the past 24 hours. This could very well be on the verge of Category 4 intensity based off satellite. ATCF upgraded to 100kt an hour ago.

 

YuJzFmw.gif

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