Hurricanes are an amalgam of the worst weather nature can produce. Not only can a landfalling storm plague entire states with intense winds, pounding rains, surges of seawater capable of flooding entire cities, but they can also spawn tornadoes. Tornadoes during a tropical storm or hurricane can be something of a hidden hazard, as they aren’t as well-advertised as a storm’s other dangers. But tropical cyclone-spawned tornadoes are no less dangerous and—even worse, they can happen with little or no warning.
It doesn’t always take a photogenic supercell on the Plains to produce a tornado. The outer bands of a tropical cyclone are ripe for thunderstorms to start rotating and quickly spawn small—but dangerous—tornadoes. There’s plenty of lift, instability, wind shear, and moisture to feed robust thunderstorms in the outer bands and allow them to rotate. Tornadoes are most common in the right-front quadrant of a tropical cyclone—that is, the area in front of and to the right of the eye’s forward motion—as that’s where wind shear is most favorable for thunderstorms to begin rotating.
Just like you would see during a more traditional tornado outbreak in the spring, tornadoes are more common in thunderstorms that are out on their own, so to speak, rather than bunched up in a squall line. Individual thunderstorms have more instability to scarf up for themselves, sometimes morphing into miniature supercells that even feature the hook echo that’s so common to see in this type of thunderstorm before a tornado.
Hurricane Harvey and its remnants spawned more than three dozen confirmed tornadoes across several states as the storm unleashed historic flooding across Texas and Louisiana. Many of the thunderstorms in Hurricane Irma’s bands spun like tops when they crashed ashore on the Florida peninsula. National Weather Service meteorologists who surveyed the damage in Florida have confirmed nine tornadoes as of September 14—eight in central Florida and one in the southern part of the state.
All of the tornadoes that occurred during Harvey and Irma were on the weaker side, but “weak” is a relative term. Even a bottom-of-the-scale EF-0 has winds strong enough to lift debris through the air, shatter windows, and knock down trees and power lines. And some of the tornadoes in a tropical cyclone can be quite strong. Hurricane Ivan’s remnants produced an unusually intense tornado outbreak as it moved inland in September 2004. The storm produced more than 100 tornadoes through the southeast and Mid-Atlantic, and more than a dozen of them caused damage significant enough that they were rated an F2 or F3 on the old Fujita Scale.
Compounding the danger posed by this type of tornado is the fact that you don’t have much time to react when a warning is issued. The typical lead time for a tornado warning—that is, the amount of time between the moment a warning is issued and the moment a tornado hits—is between 10 and 15 minutes. Sometimes the lead time is as high as half an hour, but sometimes there’s no warning at all. The thunderstorms in a tropical cyclone’s outer band are often speeding along at more than 60 MPH. That’s much faster than the speed of a normal thunderstorm, and this brisk forward motion reduces the amount of time you have to react if a tornado touches down.
The rules of survival during a tornado are the same no matter where the funnel sprouted from—get as low as possible, and put as many walls between you and the outdoors as possible. Unfortunately, not everyone in the path of a storm can heed that advice. The combination of hazards during a tropical storm or hurricane presents a unique threat to the safety of those in harm’s way. The mantra of hurricane safety is that you should hide from the wind and run from the water, and that often means getting to higher ground. But what happens when you have to worry about flooding and tornadoes at the same time?
Well, there aren’t many good options. The threat for tornadoes is among the many good reasons why people in flood zones—areas at risk of both storm surge or freshwater flooding—should evacuate ahead of time if at all possible. There were multiple instances of tornado warnings during Hurricane Harvey for neighborhoods where the water was so deep that residents were trapped in their attics and on the roof. You don’t really have anything to do in that sort of a situation, other than to hope for a swift rescue—or that the tornado misses your home. But if you’re truly trapped, your best bet is to get as low as possible without getting into the water. Once the threat passes, retreat immediately back to higher ground.
Dhoruba ni mchanganyiko wa hali mbaya zaidi ya hewa ambayo asili yaweza kutokeza. Dhoruba ya mvua ya baharini inaweza kuharibu majimbo yote na upepo mkali, mvua kubwa, na maji ya bahari yanayoweza kufurika majiji yote, lakini pia inaweza kuzalisha vimbunga. Vimbunga wakati wa dhoruba ya kitropiki au kimbunga vinaweza kuwa hatari iliyofichwa, kwani hazitangazwa vizuri kama hatari nyingine za dhoruba. Lakini vimbunga vinavyotokana na vimbunga vya kitropiki si hatari sana na hata mbaya zaidi, vinaweza kutokea bila onyo lolote au kwa muda mfupi tu. Si mara zote kuchukua photogenic supercell juu ya Plains kuzalisha kimbunga. Vipande vya nje vya kimbunga cha kitropiki vimekomaa kwa dhoruba za radi kuanza kuzunguka na haraka kuzaa vimbunga vidogo lakini vyenye hatari. Kuna mengi ya kuinua, ukosefu wa utulivu, upepo shear, na unyevu kulisha dhoruba nguvu katika bendi za nje na kuruhusu yao kugeuka. Tornado ni ya kawaida katika quadrant ya mbele ya kulia ya kimbunga cha kitropiki - ambayo ni, eneo mbele na kulia ya mwendo wa mbele wa jicho - kama hiyo ni ambapo upepo shear ni mazuri zaidi kwa dhoruba ya radi kuanza kuzunguka. Kama ilivyo katika hali ya kawaida ya vimbunga wakati wa majira ya kuchipua, vimbunga ni kawaida katika dhoruba za radi ambazo ni nje kwa wenyewe, badala ya kuunganishwa katika mstari wa dhoruba. Dhoruba za umeme za mtu binafsi zina ukosefu wa utulivu zaidi wa kujifunua, wakati mwingine zikibadilika kuwa supercells ndogo ambazo hata zina sauti ya ndoano ambayo ni ya kawaida kuona katika aina hii ya dhoruba ya umeme kabla ya kimbunga. Kimbunga Harvey na mabaki yake yalisababisha vimbunga zaidi ya 30 katika majimbo kadhaa ya Marekani, na kusababisha mafuriko ya kihistoria katika jimbo la Texas na Louisiana. Dhoruba nyingi za radi katika vikundi vya Kimbunga Irma zilizunguka kama vilele vilipogonga pwani kwenye peninsula ya Florida. Wataalamu wa hali ya hewa wa huduma ya hali ya hewa ya kitaifa, ambao walichunguza uharibifu huko Florida, wamethibitisha vimbunga tisa mnamo Septemba 14, nane katikati mwa Florida na moja kusini mwa jimbo hilo. Vimbunga vyote vilivyotokea wakati wa Harvey na Irma vilikuwa upande dhaifu, lakini "dhaifu" ni neno la jamaa. Hata ndege ndogo kama EF-0 ina upepo wenye nguvu wa kutosha kuinua mabaki ya ndege, kuvunja madirisha, na kuangusha miti na nyaya za umeme. Kwa mfano, vimbunga vinavyoitwa tornadoes vinaweza kuwa vikali sana. Mvua ya Ivan ilisababisha vimbunga vingi vya kimbunga mnamo Septemba 2004. Kimbunga hicho kilisababisha vimbunga zaidi ya 100 kusini mashariki mwa Atlantiki na kati ya Atlantiki, na zaidi ya kumi na mbili kati yao kusababisha uharibifu mkubwa wa kutosha kwamba walipimwa F2 au F3 kwenye kiwango cha zamani cha Fujita. Kuongeza hatari inayosababishwa na aina hii ya kimbunga ni ukweli kwamba huna muda mwingi wa kuitikia wakati onyo linapotolewa. Wakati wa kawaida wa kuongoza kwa onyo la kimbunga - ambayo ni, kiasi cha muda kati ya wakati onyo linatolewa na wakati kimbunga kinapiga - ni kati ya dakika 10 na 15. Wakati mwingine wakati wa kuongoza ni juu kama nusu saa, lakini wakati mwingine hakuna onyo wakati wote. Dhoruba za radi katika eneo la nje la kimbunga cha kitropiki mara nyingi husafiri kwa kasi ya zaidi ya kilomita 60 kwa saa. Hiyo ni kasi zaidi kuliko mwendo wa dhoruba ya kawaida, na mwendo huu wa haraka wa mbele hupunguza muda unaobaki wa kuitikia ikiwa kimbunga kitagusa ardhi. Kanuni za kuishi wakati wa kimbunga ni sawa haijalishi ambapo funnel sprouted kutoka - kupata chini iwezekanavyo, na kuweka kama kuta nyingi kati ya wewe na nje iwezekanavyo. Kwa kusikitisha, si kila mtu aliye katika njia ya dhoruba anayeweza kutii shauri hilo. Mchanganyiko wa hatari wakati wa dhoruba ya kitropiki au kimbunga inatoa tishio la kipekee kwa usalama wa wale katika njia ya madhara. "Mantra ya usalama wa kimbunga ni kwamba unapaswa kujificha kutoka kwa upepo na kukimbia kutoka kwa maji, na mara nyingi inamaanisha kupata ardhi ya juu. """ Lakini inakuwaje unapokuwa na wasiwasi kuhusu mafuriko na vimbunga wakati uleule? Naam, hakuna chaguzi nyingi nzuri. Tisho la vimbunga ni mojawapo ya sababu nyingi nzuri kwa nini watu katika maeneo ya mafuriko - maeneo yenye hatari ya dhoruba au mafuriko ya maji baridi - wanapaswa kuhamia mapema ikiwa inawezekana. Maonyo ya kimbunga yalitolewa katika maeneo ya karibu na eneo la Harvey, ambapo maji yalikuwa ya kina kirefu sana hivi kwamba wakazi walikuwa wamekamatwa kwenye paa na kwenye nyumba zao. Wewe si kweli kuwa na kitu chochote cha kufanya katika aina hiyo ya hali, nyingine kuliko matumaini kwa ajili ya uokoaji wa haraka au kwamba kimbunga misses nyumbani kwako. Lakini ikiwa umenaswa kweli, njia bora ni kushuka chini iwezekanavyo bila kuingia majini. Hatari inapopita, rudi mara moja kwenye mahali palipoinuka.